In 2017, the European Southern Observatory (ESO) awarded a contract for the Polishing, integration and final figuring of the Segment Assemblies of the primary mirror (M1) for the Extremely Large Telescope (ELT) to Safran Reosc. Since then, the design and commissioning of a production unit dedicated to ELT M1 has been accomplished and the plant has been producing many mirrors since spring 2022. We will introduce the smart factory, its processes and their automation that enabled reaching the current throughput of one mirror per day. We will then present the status of the project, some lessons learned and highlight the successes that have been achieved so far.

The Large Fiber Array Spectroscopic Telescope (LFAST) pursues large collecting aperture at low cost. Arrays of 0.76m, f/3.5 mirrors will focus light into fibers that are combined at a high-resolution spectrograph. The mirror substrates are fabricated from 25.4mm thick Schott Borofloat^® discs in a one week slump and polish process that leaves less than 80nm rms wavefront error in medium and high spatial frequency modes. Low-order figure errors are corrected with a perimeter ring of thermoelectric controllers that induce expansion or contraction with top-to-bottom thermal gradients. In operation, temperature variations from nighttime cooling cause time-varying aberration modes. Using feedback from a stellar wavefront sensor, these aberrations can be compensated to focus starlight energy into a 1.4 arcsec fiber.

To unlock the potential of space, there is a push for better optical imaging, including for larger parabolic on and off-axis mirrors. Costs and lead times have prohibited many programs from scaling. To answer this call, Optimax is developing manufacturing capabilities using a Lean Cell approach, where generation, polishing, smoothing, final figuring, and core metrology are centrally located and tightly controlled. This approach, and its adaptability, will allow lead time reduction from 60+ weeks to eight weeks for 0.5 m optics. Because all components are contained in one cell, ownership of results is carefully monitored by engineers and technicians from start to finish, increasing the quality and decreasing the decision-making time between steps. Finally, advances in the coating capabilities allow for a variety of customized, 0.5 m optic size coating formulations to finish the process. Data from recent projects will be shared to highlight the process and capabilities.

The prototype of Gamma-ray Cherenkov Telescope (pGCT) is an Imaging Atmospheric Cherenkov Telescope (IACT) developed to detect Very High Energy (VHE) from various cosmic sources emitting gamma rays. It is based on a Schwarzschild-Couder (SC) dual-mirror configuration resulting in a compact telescope and an optimised PSF over a wide field of view. Moreover, some innovative features were implemented with the aim to ease and to fasten the assembly, integration, test (AIT) and maintenance activities. Both mirrors, the 4-meter tessellated primary mirror and the secondary mirror, are aspherical lightweight mirrors made by a subtractive manufacturing method. This process was improved several times leading to enhanced optical performance of the telescope in terms of Point Spread Function and improved signal to noise ratio. This paper deals with the optomechanical design of the pGCT and its latest measured performance. After a brief overview of the mechanical design of the telescope, the updated manufacturing process of the new generation mirrors and the optical performance of pGCT are given. Finally, recent operational performance of the telescope is given.

In the context of the Cherenkov Telescope Array gamma-ray Observatory (CTAO), two large-size telescopes, each with a diameter of 23 m, will be installed at the southern site in Paranal, Chile. They are referred to as Large Size Telescope South, LST-S (it should be noted that 4 Large Size Telescopes, with a similar optical configuration, are already being installed at the CTAO northern side of La Palma, Canary Islands, Spain). INAF oversees the coordination of the implementation effort related to the LST-S telescopes. They will use a single mirror parabolic shape to capture images with moderate angular resolution. To achieve this shape, 198 hexagonal reflecting panels will be assembled into the telescope structure. Each panel is roughly 150 cm side-to-side in size and weighs less than 50 kg. It comprises two solid glass plates bonded to a lightweight honeycomb structure of an aluminum alloy core. The panels are spherical and distributed in three coronas with different curvature radii to achieve the desired shape. They will be exposed to the open air for several years and must withstand mechanical stresses, wind impact, and possible strong earthquake solicitations. The panels are the elements of the telescope's segmented primary mirror. The development activities for such large panels performed to optimize the mirror design and the results after the production of prototypes are summarized in this paper.

Spaced-based mirrors are a developing use-case for Additive Manufacturing (AM), the process that builds a part layer-by-layer. The increased geometric freedom results in novel and advantageous designs previously unachievable. Conventionally, mirror fabrication uses subtractive (milling & turning), formative (casting) and fabricative (bonding) manufacturing methods; however, an additive method can simplify an assembly by consolidating individual components into one, and incorporating lattice structures and function optimised geometries to reduce the mass of components, which are beneficial to space-based instrumentation as mass and volume are constrained. Attention must be given to the printability of the design - build orientation and powder/resin removal from lattices and internal cavities are challenges when designing for AM.

This paper will describe the design, manufacture and metrology of mirror prototypes from the Active Deployable Optical Telescope (ADOT) 6U CubeSat project. The AM mirror is 52mm in diameter, 10mm deep, with a convex 100mm radius of curvature reflective surface and deploys telescopically on three booms. The objectives of the designs were to combine the boom mounting features into the mirror and to lightweight both prototypes by 50% and 70% using internal, thin-walled lattices. Four final lattice designs were downselected through simulation and prototype validation. Prototypes were printed in the aluminium alloy AlSi10Mg using powder bed fusion and fused silica using stereolithography. Aluminium mirrors were single point diamond turned and had surface roughness measurements taken. Fused silica designs were adapted from the aluminium designs and have completed printing.

Reflective optical systems typically combine precise aligned mirrors, housings, interface structures et cetera. For MICADO (Multi-AO Imaging Camera for Deep Observations), a first-light instrument for ELT, Fraunhofer IOF realize several optical sub-systems, including ten freeform shaped metal optics for the Collimator, the high-resolution Imager, the low-resolution Imager and the Camera. In this paper, the challenges of freeform manufacturing and metrology will be described. For manufacturing of those mirror substrates suitable technologies, as slow tool servo (STS) and fast tool servo (FTS) diamond turning and for further correction (e.g., magnetorheological finishing) and smoothing steps (e.g., chemical-mechanical polishing), sub-aperture tools are required. For interferometry of freeform shaped optical surfaces, computer generated holograms including reference fiducials are realized. After manufacturing the mirror substrates, the optical surface will be coated with a high-reflective gold coating.

The chopper is a cryogenic tip-tilt mechanism in the Common Fore Optics (CFO) of METIS, the mid-infrared imager and spectrograph for ESO’s Extremely Large Telescope (ELT). In this paper we delve into the milling process of the mirror of the chopper mechanism, denominated as CM5. This highly accurate mirror is fully integrated into a tip-tilt mechanism and operates to reduce the background noise by shifting between the target object and the background, this happens with a frequency of 5Hz. We will primarily focus on the challenges encountered during the mirror-mechanism fabrication. Notably, the tip/tilt mechanism in the chopper requires precision levels that surpass the accuracy of the 5-axis milling machine that is used. The general accuracy of the used machine on a multi sided part is typically 20 to 30 microns, and is dominated by thermal drift of the machine itself. This significantly increases the manufacturing complexity, therefore a specialized production methodology was devised to ensure the achievement of the micron-level tolerances. In the next paragraphs we will describe how the critical tolerances of down to 5 microns in the mechanism features have been achieved. The use of a so-called Golden Sample provides a known and stable reference during manufacturing, allowing to bypass the drift and static errors of the machine. The usage of CMM measurements proves that the developed production method delivers excellent results overcoming the limitations of the machine accuracy. This monolithic aluminium cryogenic mirror has been produced through in-house CNC programming, milling, and thermal ageing followed by thermal cycling, Single point diamond turning (SPDT) and Wire Electrical Discharging Machining (Wire EDM) by external suppliers. After SPDT of the optical surface, the surface is polished to optical quality and finally a gold coating layer is applied to increase the reflectivity in the desired wavelength.

In this study, we introduce a novel approach in atomic layer deposition (ALD) for telescope mirror protection using a meter-scale ALD system (MSAS) designed for large substrates, addressing previous limitations in ALD applications for telescope mirrors. MSAS incorporates a unique reaction chamber design, allowing uniform protection coatings on 900 mm substrates. We extensively analyzed ALD of aluminum oxide (AlOx), comparing it with a wafer-scale ALD system (WSAS). Our findings reveal scalable ALD processes with optimized parameters, offering applications for silver-based telescope mirrors. For aluminum-based telescope mirrors (Al-mirrors) operating in the far UV spectral range, we explored the use of aluminum fluoride (AlFx) as a transparent protection coating. Unlike traditional ALD of AlOx, ALD of AlFx is uncommon, posing challenges in achieving a 2 nm uniform coating. Furthermore, susceptibility of Al-mirrors to oxidation complicates the coating process. Through the study and modifications in MSAS, we gained critical insights into scaling ALD processes for AlF3 protection coatings, offering unique solutions for improving Al-mirrors’ performance and durability.

The stressed-mirror polishing process has been successfully deployed to manufacture Nancy Grace Roman Space Telescope coronagraph mirrors. This process combines a simple warping system with an optimized thickness distribution of the mirror’s substrates, allowing it to warp them into the required Off-Axis Parabola parameters. This way, the polishing process uses full-sized tools, avoiding generating undesired high spatial frequency sub-aperture tool marks. The smoothness of the surface is then worked with a super-polishing process, lowering the roughness to a few Angstroms.

The research we present is done in the post-RST technology maturation roadmap frame. The Habitable Worlds Observatory requirements are so drastic that the performance of the stressed mirror polishing process needs to be improved to gain surface roughness.

Therefore, synthesizing nanoparticle slurries seems to be an alternative to aiming for a low roughness value. In this paper, we present the nanoparticle production process, the results obtained on the mirror prototypes we produced, and the roadmap for the production of hyperpolished OAPs.

The extreme and out of the ordinary sensitivity shared by the main gravitational waves detector like LIGO, Virgo and KAGRA has recently enabled to access to a new source of information for astronomy. However, future upgrades and new challenges continue to be addressed for reaching wider horizons of meas urable universe events through the gravitational waves. It leads to tighter and tighter specifications in several domains and in particular in the accuracy of the optics at the core of the detector.

For the optical surfaces of the critical optics of these detectors, the current specifications for instrumentations are not sufficient. For instance and concerning Advanced Virgo + critical mirrors (End Mirrors and Input Mirrors), the specification of their SFE (Surface Form error) is now reaching the accuracy level of one atom size, the angstrom, and for optical part up to 550 mm in diameter and 200 mm in thickness.

Besides this, the complete optical part is polished and shall have lateral reference surfaces that are at the level of usual specification of optical surfaces in astronomy.

Thales SESO is in charge of producing these uncommon optics and will present these extremely accurate optical parts, comparison of optical set-up performances as well as final performances.

Many optics applications, including x-ray synchrotron systems and space applications, require increasingly precise mirrors to enable diffraction limited focusing of x-ray beams. These mirrors require nanometer level form error and extremely tight tolerances in the mid-spatial frequency and surface roughness ranges. This talk will discuss efforts at Optimax to address this need through advancement of robotic smoothing platforms and processes. Specifically, process refinement results using a large robot, with up to a 1 meter reach, will be shared.

Mid-spatial frequency manufacturing errors are often present in aspherical optics. These errors arise from the nature of the asphere manufacturing process, whereby many passes are made on multi-axis polishing machines with subaperture sized tools. The process results in mid-spatial frequency artifacts which can typically be characterised into 2 types of form error: rings and spokes. The standard tolerance specifications of form and slope error used in asphere manufacture does not capture the range of possible outcomes for an as manufactured part. The fact that the current tolerance standard does not adequately describe the range of outcomes for as manufactured aspheres has been known for some time. In this work, we present a set of basis functions which represent rings and spokes, combined with statistical form errors sampled from an appropriate power law statistical distribution in frequency space. We use real data to verify that our error representation is more efficient mathematically as compared with the standard Zernike decomposition.

We propose a method to analytically design optical systems achieving a wide field of view (FOV) by freeform surfaces of minimum gradient based on the aberration theory of off-axis optical systems and freeform surfaces. By the method, an F/3 and 200 mm aperture-class optical system with three mirrors was designed that achieves a diffraction limit of 587 nm over a FOV of ϕ4.54 degrees. The maximum gradient of the freeform surfaces on the primary, secondary, and tertiary mirrors are 89, 98, and 94 mdeg, respectively. The maximum gradient of the freeform surfaces is reduced by 46% compared to the optical system designed in the previous study with the same specifications. Our method guarantees the minimum amount of the gradient of the freeform surfaces, which cannot be guaranteed by the conventional design method using optimization by ray-tracing software.

The field curvature has been a long-term problem optical designers had to deal with, to propose flat corrected field instruments. Combinations of highly aspherical optics, TMA configurations, achromatic doublets or field flatteners are often used to reach good optical quality across the image. Allowing designers to play with the parameters of the field’s shape is offering them a brand-new game field. The possibility of curving the CMOS sensors to fit curved/aspherical/freeform shapes of focal surfaces has been studied for the last 20 years and led today to different applications and prototypes. We present in this article 1/ the parameter studies we performed over a large set of optical designs showing the gain offered by this approach, 2/ the CMOS sensors curving process and performance over a large set of prototypes, 3/ Optical systems that have been produced with this technology and 4/ the roadmap related to the development of curved-sensors based instrumentation for astronomy with the CASTLE telescope project and physical sciences through the Auroral UV Imager program led by ESA.

Dimensional changes of mirrors under spaceborne irradiation must be considered in the context of increasingly narrow tolerances. Among those factors impacting the optical figure, thermal transients are one of the main reason accounting for deformation, thus this is the reason why low CTE material (ZERODUR®) and/or heat diffusive material are exclusively considered for these applications. Radiation induced compaction can play a role in dimensional stability. This compaction effect is due to the local change of density induced by the collision of energetic particles (e.g. protons and electrons trapped in the Van Allen belt) with the mirror substrate. To address this perceived problem, we performed numerical evaluation of the irradiation levels expected over four different orbits (LEO, GEO, Sun Synchronous, L2) as seen by a ZERODUR® primary mirror. From these orbits, we then selected the harshest Earth-Orbiting conditions, namely those at GEO, and performed an equivalent lab-based e- and H+ irradiation. The effects of radiation induced deformation (compaction) onto the coupons have been then measured interferometrically for change. Finally, using our laboratory irradiation results and following a rigorous mechanical approach, we propose a upper bound for the expected deformation that would be expected with a baffled spaceborne lightweighted telescope. The negligible deformation derived in this study are consistent with decades of successful missions using ZERODUR® mirrors.

Kyocera Fine Cordierite (CO720) is a highly promising material for optical mirrors and structural components for space applications due to its excellent properties such as high rigidity, low thermal expansion, and high thermal conductivity. It has already demonstrated its performance in space applications and is begin considered for adoption in many future projects. However, detailed material property data of Fine Cordierite in the space environment has not been made publicly available. Therefore, despite its excellent characteristics, there is a prevailing hesitation to adopt it actively in ongoing or planned projects. In order to address this issue, we have prepared Fine Cordierite test samples and conducted ground tests that simulated the prominent effects of radiation (γ-ray) and atomic oxygen exposure in the space environment and compiled the results into a database. This database includes mechanical properties (bending strength, Young's modulus, and bulk density), thermal properties (coefficient thermal expansion and thermal conductivity), and optical properties (surface accuracy) before and after applying radiation and atomic oxygen exposure. In the presentation, we will discuss the availability and practicability of Fine Cordierite in the space environment, comparing the inspection results of low thermal expansion glass and glass-ceramic conducted at the same time.

A new deposition method developed by Goddard Space Flight Center fluorinates Al mirrors with XeF2 followed by a LiF coating to create what they term Al+XeLiF. This in-situ, room temperature process produces mirrors with high reflectivity in a broad spectral range, from the FUV to the IR, and is reported to be stable in relative humidities of 30% and lower. These mirrors are envisioned for missions requiring sensitivity down to 100 nm wavelength such as the habitable worlds observatory. Because most mission integration and testing campaigns require prolonged exposure to lab environments, and launch sites experience high relative humidities (RH) on average, some at 80% RH. We investigate Al+XeLiF stability in a wider range of temperatures and humidities along with employing additional characterization techniques including atomic force microscopy and x-ray photoelectron spectroscopy. We found that Al+XeLiF is stable in environments up to 82%RH when kept at cooler temperatures (3°C and 21°C). However, this material is unstable when stored at 60°C, experiencing roughening and loss in reflection from resulting Al surface plasmon excitation.

The effects of Fe and Mn on the thermal expansion characteristics of non-ferromagnetic Cr-Fe-Mn alloys, which exhibit the Invar effect, were investigated. It was found that the temperature range in which the alloy exhibits low thermal expansion characteristics is below 273 K when the Mn content is less than 0.3%. Conversely, this range shifts to between 273 and 350 K when the Mn content increases to 0.9% or higher. By incorporating small amounts of rare earth elements, the Cr_94.6Fe_4.7Mn_0.7 alloy achieved an average coefficient of thermal expansion of 0.94 × 10⁻⁶/K between 273 and 350 K, which is lower than the 1.2 × 10⁻⁶/K observed in conventional Invar alloys. Additionally, measurements of magnetic hysteresis loops were conducted to assess the residual magnetization, which is critical for structural components near magnetic measurement equipment. The results indicated that the residual magnetization of the Cr-based Invar-type alloy is approximately 0.0033 mT, significantly lower than the 35 mT typically found in conventional Invar. These substantial differences underscore the potential of Cr-based Invar-type alloys as a superior alternative for applications requiring low thermal expansion and low residual magnetization.

Several near-infrared instruments on upcoming extremely large telescopes use a combination of OHARA S-FPL51 and S-LAH71 glass prisms to correct for the atmospheric differential refraction. Because large parts of these instruments are contained within a vessel cooled to liquid nitrogen temperatures, the changes in optical and mechanical properties should be considered during the design phase.

In this report, we provide an update to our continuing efforts to characterize the S-FPL51 and S-LAH71 glass under cryogenic conditions. These efforts include a measurement of the refractive index (293 K, 100 K and 80 K), transmission measurements (293 K, 77 K and 43 K) and a determination of the coefficient of thermal expansion (between 293 K and 45 K). We will describe the cryogenic test setups that we have used to obtain our results, and provide summarizing equations of these material properties.

This characterization will prove useful for conceptual design trade-offs, mechanical interface solutions and detailed optical design for future near-infrared instrumentation on large telescopes.

Since the fabrication of the Keck telescope primary mirror segments, radius of curvature matching have been known to be one of the major challenge in manufacturing segmented optics with high accuracy. Curvature is generally not a critical specification for optics as any error can be compensated by alignment (for a telescope mirror, by the distance between M1 and M2). However, for a segmented primary such as the ones in the Keck, GTC or ELT telescopes, a radius of curvature mismatch prevents from generating a continuous surface when assembling the mirror through a residual surface error called scalloping. We will present how this constraint drove the design of ELT metrology means, and how we achieved a radius of curvature metrology with 50 ppm absolute accuracy on a 71m curvature reference.

In this effort, we demonstrate the performance of a highly stable time reference for the proposed Black Hole Explorer (BHEX) mission, a space-based extension to the Event Horizon Telescope (EHT) Very Long Baseline Interferometry (VLBI) project. This precision timing system is based on the use of a space-qualified, ultralow noise laser developed as part of the Laser Interferometer Space Antenna (LISA) mission as the timing reference, and an optical frequency comb to transfer the stability of this laser to the microwave regime for instrumentation use. We describe the implementation of this system and experimental setup to characterize the stability performance. We present the results of this experiment that demonstrate the performance of this system meets requirements for the BHEX mission.

Tunable laser frequency combs that can map the point spread function across a spectrograph’s entire bandwidth are necessary for improving the instrumental systematics to reach near-infrared radial velocity precision levels < 1 m/s. We demonstrate a scannable 30 GHz electro-optic (EO) comb by tuning a combination of laser center frequency and mode spacing. This tandem tuning is necessary to avoid cavity-comb mode walk-off in a Fabry-Pérot cavity, which is used to suppress the broadband noise between the comb lines. This tuning is well-described by modeling the transmission of the EO comb through the cavity, and the entire supercontinuum spanning 700 – 1350 nm remains unchanged across the 30 GHz tuning range. We intend to implement this tunability for the 30 GHz EO comb deployed at the Habitable Zone Planet Finder (HPF) spectrograph.

High-resolution echelle spectrographs are critical for modern astronomy. Determining their wavelength solution is a prerequisite calibration, conventionally performed by illuminating the instrument with a broadband hollow-cathode lamp and cross-referencing the resulting two-dimensional spectrum to an emission-line atlas. Challenging requirements for nextgeneration spectrograph calibration are driving the adoption of laser frequency combs in place of lamps. Laser frequency combs offer an exceptional relative calibration scale, but the task of wavelength-tagging individual comb modes currently makes a spectral-line source essential for absolute calibration. Here, we present a new approach that utilizes a laser frequency comb as the sole calibration light source. An ancillary “spectral shaping” spectrograph can excise an individual comb mode and measure its wavelength, which can then be refined to provide sub-fm accuracy wavelength tagging on a proxy astronomical spectrograph echellogram. In a secondary procedure, a comb mode is isolated for each of the echellogram orders in a single measurement, revealing the free spectral range and allowing the order-to-order relationship to be established. These complementary techniques allow the complete calibration of a spectrograph to be achieved using only a laser frequency comb, eliminating reliance on auxiliary light sources and providing direct access to GPS-referenced accuracy.

The instrumentation plan for the ELT foresees the ArmazoNes high Dispersion Echelle Spectrograph (ANDES). The ANDES-project and consortium entered phase B in January 2022 and underwent several (internal and external) revisions by now to ensure that the requirements and eventually the challenging goals can be met by the physical design of the spectrograph.

Among its main scientific goals are the detection of atmospheres of exoplanets and the determination of fundamental physical constants. For this, high radial velocity precision and accuracy are required. Even though the ANDES-spectrograph is designed for maximum intrinsic stability, a calibration and thus a calibration unit is mandatory. To allow for maximum flexibility and modularity the calibration unit is physically split into three calibration units.

We show the design of the calibration units and their individual components, where possible. This includes the electronics, the mechanics, the software supporting and controlling the light guiding and calibration sources.

MOONS is the Multi-Object Optical and Near-IR Spectrograph for ESO’s Very Large Telescope. The instrument will use ∼1000 optical fibres which can be individually aligned to on-sky targets across a field of view of 500 square arcmin. Each fibre is positioned using a dual arm theta-phi fibre positioning unit (FPU). The MOONS metrology system must be able to simultaneously measure the position of each fibre to a high accuracy (∼15 micrometres) as well as measuring the orientation of the FPU arms. In this paper, we present a description of photogrammetry-based metrology system design and its implementation in the instrument. We also report on the integration, testing, and performance of the system within the instrument.

The Keck Adaptive Secondary Mirror (KASM) project will broaden the use of adaptive optics on the Keck I telescope by integrating the correction device into the secondary mirror. By replacing the static secondary with a high-actuator count convex deformable mirror, image sharpening will be available to all instrument ports. The KASM optical surface will be a thin shell polished to match the optical prescription of the existing Keck I secondary mirror to within a few microns. The final correction of the optical shape will be achieved with control of the ASM’s actuators. The calibration and verification equipment (CAVE) will be an optical metrology package designed to verify that the delivered KASM has the correct optical figure. CAVE will also be used to verify and calibrate the actuator motion, both spatially and temporally, forming the basis for the actuator influence functions used in closed-loop operations. CAVE will be used during testing at the University of California Observatories optical laboratory, as well as during commissioning and periodic verification at the W.M. Keck Observatory, necessitating a robust and repeatable kinematic mounting arrangement. We describe the design of CAVE and develop a concept for laboratory and telescope facility operations and calibration.

We designed and manufactured two OGSE dedicated to the alignment of the EUCLID telescope. These two wavefront-based platforms, set on hexapods, have been used to measure the transmitted WFE in the VIS path and the NISP path of the EUCLID payload. We present the OGSE and more specifically the Imagine Optic R-FLEX platforms. Some wavefront error maps obtained by ADS team during the AIT campaign in Toulouse are discussed.

Stray light testing is a crucial step in the development of space optical instruments, ensuring that designs perform as theoretically predicted and are free from unexpected stray light effects. Beyond this verification, stray light testing also generates kernels for stray light correction algorithms. Traditional stray light testing methods, while essential, often fall short due to their binary pass/fail output and increasingly stringent stray light requirements. To address this limitation, we have developed and demonstrated the Time-of-Flight (ToF) method for stray light characterization. Our initial application on a simple three-lens system showcased the method's potential for comprehensive stray light assessment, effectively deriving the origin of individual stray light contributors. This paper presents the latest advancements in the ToF method, highlighting its successful application in the test campaign for the NAC instrument, designed for returning samples from Mars in the frame of the Earth Return Observatory mission. Additionally, we will discuss the ToF method's effectiveness in characterizing a stray light baffle, demonstrating its broader applicability.

We developed a new opto-mechanical tool to quickly align an optical beam to a reference mechanics. In the alignment of the SOXS Common Path, one of the sub-systems of the SOXS instrument, we used a referenced (and characterized) detector to align the master laser beam to the mechanical structure of the subsystem, and to place and align individual opto-mechanical components to the master laser beam. Based on that experience, we conceptualized and prototype a new effective and much more efficient and easier to handle tool for alignment. A sphere is 3D printed to host a small bare-board CMOS detector with the sensor plane passing through the center of the sphere. This tool used in combination with a portable Coordinate-Measuring Machine (pCMM) allows for a quick alignment of a narrow collimated laser beam or a converging beam on an optical bench as in 3D space. We describe the design, prototyping and test of this new alignment tool.

TMT adopts Stressed Mirror Polishing (SMP) technology for the polishing of mirror segments. In this process, the meniscus type spherical shape glass blanks are converted in to a desired aspheric shape by spherical grinding and polishing in the stressed condition. After each grinding and polishing activity metrological measurements are done using different metrology tools. The metrology tool named as 2D-Profilometer is used for low frequency error/foam measurements. It consists of 61 high precision length gauges attached to Carbon Fiber Reinforced Polymer (CFRP) sandwiched Aluminum panel of diameter 1.6 meter in spiral direction. The coefficient of thermal of CFRP is very low however, a small delta temperature variation between the top and bottom sheet of CFRP of the panel will lead to panel bowing which will result in increasing power error. Hence, the objective this work is to analyse the thermal sensitivity of the 2D Profilometer.

This conference presentation was prepared for SPIE Astronomical Telescopes + Instrumentation, 2024.

Small Aperture Telescopes of Simons Observatory aim to detect the primordial B-mode power spectrum in Cosmic Microwave Background. For the precise measurement of the B-mode, we need to reduce systematic errors from the miscalibration of the polarization angle of transition-edge sensors. We have developed a calibrator using Sparse Wire Grid (SWG). It can calibrate all the detectors at the same time and allows us to extract information on polarization angle, time constant, and polarization efficiency. In this conference, we will present the calibration method and results using SWG.

Leighton Chajnantor Telescope (LCT) will be moved from the summit of Mauna Kea, Hawaii to Chajnantor Plateau, Chile. At the new site, strong wind load will cause structural deformation of LCT’s reflector antenna and hence influence its electromagnetic (EM) performance significantly. Radiation pattern is an important indicator of the EM for a reflector antenna and will also be greatly affected by structural deformation. For accurately and rapidly compensating for the affected EM of LCT’s reflector antenna, it is essential to develop a quick calculation method for radiation pattern analysis under varying wind loads based on our previous work on the effect of gravitational load on radiation pattern. In this paper, we propose an approximate calculation method for the optical path difference (OPD) due to the deformation of LCT’s reflector antenna under wind load. Then a mathematical formulation based on modified Zernike polynomials is presented to fit the calculated OPD. Finally, the radiation pattern will be obtained by the aperture field integration method. Numerical experiments demonstrate the effectiveness of the proposed quick calculation method for analyzing the radiation pattern of LCT’s reflector antenna at its highest working frequency. In comparison with the numerical simulation by physical optics (PO) and physical theory of diffraction (PTD), the proposed quick calculation method exhibits high accuracy for the performance criteria of the radiation pattern and reduces the time consumption for radiation pattern analysis significantly.

As part of our ongoing research and development activities for the Planetary Camera and Spectrograph (PCS) for ESO’s Extremely Large Telescope (ELT), we are comparing two types of integral field unit concepts—an image-slicer and a lenslet-array—for its integral field spectrograph and main science instrument. In our 2022 publication we described the design and manufacturing of the image-slicer used in this comparison, based on the concept of our twisted image slicer published in 2014; in this paper we present recent interferometric measurements of the mirrors of the image slicer, manufactured by Canon Inc. Using our 6-inch Fizeau interferometer we measured the spherical pupil mirrors, resulting in a typical peak-to-valley surface figure error of ≲ 160 nm, and an RMS error of ≲ 25 nm. Measuring the 0.3 mm×13.5 mm parabolic slicing mirrors was challenging, however, after removing low-order alignment errors our measurements indicate a surface error of RMS ≲ 70 nm. Based on these measurements we conclude that the surface quality of the mirrors is excellent and well suited for our experiment.

TNO and partners at University of Hawai’i (UH), the NASA InfraRed Telescope Facility (IRTF), and the Center for Adaptive Optics (CfAO) at UCSC have been working on the realization of a 244 mm Adaptive Secondary Mirror (ASM) for the NASA IRTF called the IRTF-ASM-1. After successful performance testing of several laboratory prototypes, this project provided the first on-sky demonstration of TNO’s ASM technology at M2 location with an optically powered mirror shell.

The ASM is designed to retrofit the current passive M2. The ASM consists of a 244mm-diameter slumped convex aspherical mirror shell, manipulated by 36 hybrid variable reluctance actuators mounted on a light-weighted backing structure. The mirror shell is manufactured to the required accuracy at reduced cost through slumping by UCSC. The mirror shell is finished to final figure with Magnetorheological Finishing (MRF) by TNO before it was coated.

The ASM was shipped to UH in Hilo in February 2024, where performance was tested in the lab. The IRTF ASM saw ‘first light’ on telescope on the 23^rd of April, already achieving stable closed-loop performance that was diffraction limited at the H-band (1.62 microns) with a long-exposure Strehl ratio of 35%-40% in sub-arcsecond seeing during the first night.

This paper will report on the status and first results of the IRTF ASM, including the latest status of the deformable mirror technology at TNO and an outlook to a second generation IRTF ASM with improved dynamic performance and increased actuator count.

Adaptive optics systems that use adaptive secondary mirrors can potentially broaden the use of AO in astronomy. However, unlike post-focal plane AO systems, ASM-based AO systems require large (200-1500 mm diameter), curved, aspheric membranes to replicate the standard telescope secondary mirrors that they replace. A key limitation of current devices is the cost (and associated risk) of manufacturing thin (2-3 mm) curved facesheets. We have developed a new approach for the fabrication of these facesheets that initially uses flat, polished sheets of glass that are formed into curves via heating. This technique traditionally relies on an accurate negative form to slump the glass into. We take a different approach of letting the glass slump freely within a support ring that is outside the final optical diameter of the shell. Such an approach allows for the creation of shells over a variety of radii of curvature, simply by adjusting the peak temperature. However, to create an approximately parabolic shape, an additional force is required, which can be applied by weights added on to of the shell. We have tested this over a variety of size ranges from 300-600 mm, and for a range of radii of curvature from 1000-5000 mm. We report on the fabrication of shells for the IRTF ASM, as well as initial experiments for a shell of 620 mm diameter.

Instrument rotators provide high accuracy instrument rotation at a commanded angle to ensure telescope pupil tracking. Structural support and mechanical interfaces must be provided and services (electrical and communications subsystems) routed from the stationary platform to the rotating platform for heavy instruments (which can exceed 1,500 kg). Cannot transmit vibrations to instruments. The experience gained over the years in working with several types of rotators is summarized in this paper. Not only experimental methods, but also mechanical and control models have allowed us to understand the system in depth. The paper focuses on rotators with two servomotors working together to counteract backlash and rotators with directly coupled motors. For the latter, balanced and unbalanced loads are studied. The mechanical model used to control the servo is explained and analyzed. During the development of the study, different rotator work schedules will be investigated. Tracking will be the focus of the study. The HARMONI rotator and the QUIJOTE telescopes (telescopes built by the Spanish company IDOM) in operation at the Teide Observatory (Tenerife) will therefore be the focus of our attention.

The TOLIMAN space telescope is purpose-built to probe our stellar neighbourhood for potentially habitable Earth-like exoplanets. Our novel diffractive pupil design will allow TOLIMAN to detect extremely subtle changes in the positions of stars in a binary system, down to the microarcsecond scale. One of the many challenging factors in the detection of this diminutive astrometric signal is instability in the telescope pointing, known as jitter.

This work demonstrates the capability of mitigating the blurring effects of telescope jitter through a forward modelling approach and a new precise optical positioning system. We utilise ∂Lux – a cutting-edge differentiable optical simulation framework built in Jax by our team at the University of Sydney – to model the effects of telescope jitter on the final image. The demanding stability requirements have also inspired innovative engineering approaches, including the design of a piezo-driven tip/tilt system. This methodology enables us to recover the crucial astrometric parameters despite telescope pointing instability, offering TOLIMAN the unique opportunity to observe exoplanetary signatures with unprecedented precision.

This article presented the design improvement based on the modal frequency shifting method for resolving the structural response excitation of a catadioptric telescope. For the high image quality demand optical system, the positioning stability of optics is crucial. Taking the catadioptric telescope for example, the most sensitive part is the position of secondary mirror within several micrometer tolerance along optical axis. Therefore, the opto-mechanical design for maintaining the positioning of optics while the system suffering from the harsh environmental vibration becomes important.

The aperture size of a space telescope faces constraints dictated by the dimensions of the launch vehicle, resulting in a limited aperture size. This reduction, in turn, imposes limitations on optical resolution and the signal-tonoise ratio of the space telescope. To address this challenge, deployable optical payloads equipped with segmented primary mirrors that unfold, enable larger synthetic apertures and enhanced spatial resolution while benefiting from a smaller, cheaper launch vehicle.

This paper investigates the potential of leveraging Additive Manufacturing (AM) and Topology Optimization (TO) for ultra-precision machining applications, with a specific focus on single-point diamond machining. The primary objective is twofold: to concurrently diminish fixture weight and increase stiffness. This dual approach aims to mitigate deformations induced by rotational and cutting forces, two effects known for their influence on the mirror surface form error and consequently on the optical performance. Using Finite Element Analysis (FEA), the study systematically compares fixtures produced through conventional machining (CM) with those employing AM and TO techniques. The results underscore a remarkable 68% reduction in weight for fixtures designed through TO. This substantial weight reduction renders the assembly of a machining fixture with four deployable segments of diameter 600mm when deployed, manageable by a single operator without the necessity for specialised lifting equipment. Additionally, these designs contribute to significant reductions of up to 87% and 37% in deformation caused by rotational and cutting forces, respectively. Overall, these advantages offer a promising perspective for overcoming limitations in space astronomical or Earth Observation telescope apertures.

The upcoming increased launch capacity of larger and more powerful rockets opens doors for the development of large space telescopes that would not require the mechanical deployment of optical structures in space. The University of Arizona is currently working on a space-based telescope concept that would use a 6.5 m monolithic borosilicate primary mirror typically seen in ground telescopes. Borosilicate presents manufacturing advantages but has a higher coefficient of thermal expansion than materials typically used in large space telescopes, thus requiring more precise thermal control. The observatory would be in either a highly elliptical Earth orbit, an Earth-trailing orbit, or on Earth-Moon Lagrange point 2. The telescope will require great thermal stability, so each potential orbit brings a different set of thermal requirements and leads to different modeling constraints. This paper presents preliminary thermal analyses to determine the bounds of the mission requirements, allowing the team to design a telescope that will meet the required thermal stability constraints. We are performing orbital analyses in Ansys, merging STK and thermomechanical models to calculate the heat flux from external sources, such as the sun, and estimate the heat losses to the environment. We will use the model to understand the effects of the thermal environment on the telescope mirrors and check for their survivability and optical stability under the given conditions. We will perform iterations on a mechanical design and evaluate the impacts of different passive and active thermal control systems on the thermal stability of the mirrors.

Positioning systems for optical metrology applications are continuously challenged to maintain high resolution, accuracy, and repeatability over ever-expanding ranges of motion and payload masses due to the need for larger optical apertures and sensor field of regard. To address these demands, new facility capabilities have been developed for the X-Ray & Cryogenic Facility (XRCF) at the NASA Marshall Space Flight Center. These upgrades included re-purposing the center of curvature optical bench (CoCOB) hexapod, originally designed for James Webb Space Telescope program testing, to provide precision positioning of large test articles. To maximize the potential range of test article sizes, and ultimately the utility of the facility, studies were undertaken to evaluate the maximum payload capacity and simultaneous range of motion combinations of the CoCOB hexapod without requiring significant hardware modifications. The analytical tools developed to assess and display the possible range of motion combinations for various center of rotation locations are discussed along with the results of the study. A hexapod load study was also completed to determine maximum allowable payload mass across a wide array of possible hexapod poses. Modeling was used to assess unmeasured deflections as a function of the displacement away from the hexapod’s null position and the associated impact on accuracy performance. The methodologies and results of each of these studies are presented in detail. Software techniques to prevent collisions between internal hexapod geometry and avoid overtravel of both actuator stroke and end-joint angular travel ranges are also discussed.

COSMO Large Coronagraph (COSMO LC) is a telescope dedicated to the measurement of the Sun magnetic field. This project is currently at a design phase funded by the National Science Foundation under the technical direction of the High Altitude Observatory.
COSMO LC is a refractive telescope whose objective lens has a clear aperture of 1.4m, it will be the largest refractive telescope in the world. This telescope can observe the Sun corona thanks to the internal occulter which is able to obscure the solar disk. This device needs to accomplish two main functions: 1) adapt its diameter to the Sun apparent size, 2) reject all the incoming heat to not start any air turbulence which leads to the degradation of image quality (seeing).
Diameter change is accomplished by means of a cam mechanism which actuates 14 petals arranged azimuthally while the occulter cooling is obtained through cold water running through internal channels and forced air convection.
This article describes the mathematical models employed to quantify the seeing effect on image resolution and the technical solutions adopted to implement the above-mentioned functions. In addition, the tests performed on this device are described along with the results.

Presently TNO/Demcon are manufacturing nine Laser Projection Systems (LPS). TNO is responsible for the design and manufacturing of the Optical Tube Assembly (OTA), the baseplate and the LPS cover. Demcon designed and manufactured the Beam Conditioning and Diagnostic System (BCDS). TNO is also responsible for the system performance and its verification tests.
Six units will be used on the ELT. The other three are destined for the VLT. That will allow the operation of the adaptive mirrors enabling unprecedented image quality of the telescopes. The design of this system is based on the four laser guide stars units as used on the VLT.
The system has been upgraded considerably compared to the units used for the VLT. Its FOV has increased to 7 arcmin (half cone). The laser power goes up to 50W and the BCDS has been completely redesigned. The BCDS is located between the laser source and the OTA that produces the Ø300 mm output beam. Maintainability and accessibility of the system have also been much improved.
Prime qualities are its insensitivity to temperature changes (static and dynamic), its accuracy and its FOV. Assembly of the first unit is finished and in January the acceptance testing of the system started. The first unit is expected to be delivered to ESO in autumn 2024.

Safran Reosc was awarded the manufacturing of the Secondary Mirror of the Extremely Large Telescope by ESO in 2016. The secondary mirror is a 4-meter convex mirror, the world’s largest convex precision mirror ever made. As of spring 2024, this mirror is in its final phase of polishing. It is regularly controlled on a dedicated interferometric test bench (ITB) specifically designed to achieve the best accuracy on such a large mirror. The test bench was thoroughly validated in September 2023 and all its requirements were demonstrated. This bench includes a convex-concave test plate together with a unique custom interferometer system, both specifically designed and manufactured for this test bench. In fact, the specific requirements of this very large mirror forbid the use of off-the-shelf component or interferometer and it was necessary to design a specific interferometer to cope with all the requirements. Furthermore, it was necessary to manufacture an almost perfect 2-m reference plate to control the mirror. It took about 3 years to manufacture this reference plate with the requested accuracy.

The test bench makes a measurement on 24 sub-pupils which are stitched together to reconstruct the final surface error. The full aperture measurement and the map stitching lasts around 2 hours. Specific sensors are used to monitor the stitching process and the stitching algorithm had to be adapted in order to fulfil the stringent performance requirements.

In this paper, we present the main features of the bench, the alignment strategy, the test results obtained on the bench and the stitching algorithm developed to reconstruct the surface error.

As telescopes dramatically increase in aperture, the size and complexity of instrumentation also increases dramatically. Simply scaling up existing spectrograph designs may not be feasible and new approaches must be considered. One alternate approach is multiplexing, where the high cost of large optics is replaced by smaller, lower-cost optics albeit in higher quantities. While the idea of large-scale multiplexed instruments is not new, ELTs push the scaling of instruments into territory where multiplexing may have significant advantages. However, it remains to be seen if optical mounts can be made to meet the ever-tightening optical requirements of modern instruments while retaining the low-cost and ease of use required to make multiplexing a feasible approach.

This paper details the design, prototyping and testing of several types of low-cost semi-kinematic optical mounts at NRCHerzberg from a practical standpoint. Optical mounts tested cover a range of types intended to be easy to manufacture, quick to assemble and suitable for various instrument environments. Assembly repeatability in tip/tilt/focus, assembly time, and wavefront error due to stress birefringence (simulated) are quantified and results presented. Thermal stability, suitability for use in cryogenic environments and ease of manufacture/assembly are also analyzed. Various qualitative metrics are also discussed. Quantitative and qualitative metrics are discussed and presented in a design table to aid in directly comparing lens mounting concepts. Results are also interpreted to determine the direction of future R&D efforts towards creating large-scale, multiplexed instruments.

Arrayed Wide-Angle Camera System (AWACS) is based on segmented-field corrector architecture and can be scaled to a much larger than meter-size field of view featured in Extremely Large Telescopes (ELTs). In essence, the AWACS accomplishes desired field expansion via a suite of small cost-effective electro-opto-mechanical units over a telescope’s focal surface, for local and simultaneous telescope field aberration and atmospheric dispersion compensation (ADC). In our previous report, we summarized the architectural features and design examples of the AWACS and discussed the snapshots of the components/subsystems of the AWACS-Duo at various development stages. In April 2023, we had a first on-sky run on the 2.7m Harlan J Smith Telescope to commission the rest of the system functionalities. The on-sky commissioning included verifying the guiding and acquisition, imaging performance and field aberration compensation across 1.2-degree telescope field, the ADC operation and performance, and throughput consistency between two AWACS units, all with respect to the model expectations. This report summarizes the results from this commission effort and the plan forward.

In ground-based mid-infrared observations the background radiation must be removed. Chopping is a background removal method requiring fast switching of the observation field. For MIMIZUKU, the mid-infrared instrument for the TAO telescope, we have developed a cold chopper which switches the observing field by tilting a movable mirror inside MIMIZUKU, instead of tilting the large secondary mirror. We require a short transition time, sufficient amplitude, high frequency and steadyness for observation in the chopper movement. With Repetitive Control we significantly increase performance by iteratively improving a feedforward trajectory and continously adapting to changes in the nonlinear dynamics. This allows for much shorter transition time (<30 ms) and more freedom in the design of a feedback controller. Furthermore, repetitive disturbances originating from the cryo-cooler can be countered thus improving stability on sky. Controller design, stabilisation, choice of reference trajectory, real-time computability and performance trade-offs are subjects in this research.

The large class science mission NewATHENA, rescoped by the European Space Agency (ESA) in November 2023, will explore the hot and energetic universe using advanced X-ray technology. The key components of the telescope will be hundreds of Silicon Porous Optics (SPO) modules arranged in an optical bench with a diameter of around 2.7 metres. Considering the overall size, the delicate cell structure and the high aspect ratio in combination with the material-related challenges of Ti6Al4V, additive manufacturing using Direct Energy Deposition (DED) is a promising alternative to conventional processing. In addition to discussing fundamental challenges (e.g. shielding), the development of a highperformance hybrid DED process and associated equipment for robust long-term production will be presented. The developed end-to-end manufacturing approach will be verified by manufacturing and analysing test specimens, geometric demonstrators and representative large breadboards [1], [2].

This paper reports on a nested freeform Three Mirror Anastigmat (TMA) telescope designed for a 3U CubeSat, achieving a compact 1.5U form factor with a focal length of 500mm, F/4.6. Capable of near-diffraction-limited performance in a 0.37°x0.42° field of view, it provides 5m Ground Sampling Resolution in Low Earth Orbit. The paper explores two housing options: one for additive manufacturing (AM) and the other for conventional machining (CM), aiming to determine the optimal approach for creating an AM-based optical system housing suitable for space. The AM option offers lightweighting opportunities and enhanced structural integrity. The mirrors, manufactured in RSA 443 with Nickel Phosphorus plating, alongside the AM material, AlSi40, are discussed for their homogeneous coefficient of thermal expansion crucial for orbital conditions. The paper reports on the AM process, system metrology, and high precision finishing through Ion Beam Figuring.

Additive Manufacture (AM) comprises a group of technologies that allow to go from a 3D model to manufactured components, creating them layer by layer until the part is complete [1]. Among the advantages of AM, the ones that apply most to astronomical instrumentation are part complexity and consolidation, the addition of functionalities, design freedom and lightweighting capability.

The IAC participated in the H2020 international consortium, within the work package on cooled mirrors for astronomical instrumentation [2], whose completion in 2021 left a series of outputs in terms of preferred technologies and materials, lightweight typologies and a cookbook [3] that includes both design guidelines for additive manufacturing and specific values of the geometrical parameters for the parts to be "printed".

The aim of this paper is to present the whole process since the beginning: from the conceptual design, to the results of the studies carried out on the lightweight mirror samples (with the two typologies and the most promising materials of those studied within the IAC for H2020). Comparisons will be made mainly in terms of metrology, dimensional tolerances and optical surface finishes of the mirrors (roughness, SFE, etc.).

Despite the established role of additive manufacturing (AM) in aerospace and medical fields, its adoption in astronomy remains low. Encouraging AM integration in a risk-averse community necessitates documentation and dissemination of previous case studies. The objective of this study is to create the first review of AM in astronomy hardware, answering: where is AM currently being used in astronomy, what is the status of its adoption, and what challenges are preventing its widespread use? The review starts with an introduction to astronomical instruments size/cost challenges, alongside the role of manufacturing innovation. This is followed by highlighting the benefits/challenges of AM and used materials/processes in both space-based and groundbased applications. The review case studies include mirrors, optomechanical structures, compliant mechanisms, brackets and tooling applications that are either in research phase or are implemented.

Despite images of the solar corona in selected bands of the electromagnetic spectrum have been regularly acquired for years, several key questions on its physics and chemistry are unanswered. In order to properly undertake a comprehensive physical study of the solar corona, it is mandatory to investigate its emission lines. Several spectrometer have been investigating the solar corona over the solar disk. The only UV coronagraph/spectrometer flown so far, that has continuously observed the extended solar corona out of the solar disk (from 1.5 R_⊙ to 5 R_⊙), is UVCS (UltraViolet Coronagraph Spectrometer), operative from 1995 to 2009 aboard the SOHO (Solar and Heliospheric Observatory) mission. It was characterized by a 40 arcmin linear slit tangent to the solar limb, moved at different heliocentric heights by means of a tiltable mirror. Different polar angles were explored by rolling the whole instrument. Despite the milestone results it successfully provided, UVCS was not suited to follow the solar corona dynamics: coronal phenomena may evolve on times that range from minutes to hours, while a complete coronal spectrocopic map at full resolution took about 1 day for UVCS to be acquired. A circular slit with variable radius coupled with a grating having circular concentric grooves would reduce by at least 1 order of magnitude the time range needed for mapping the whole solar corona spectrum and would therefore be ideal for performing spectroscopical studies of the UV/EUV dynamics of the solar corona. CISS (CIrcular Slit Spectrometer), funded by the Italian National Institute for Astrophysics (INAF), is a project dedicated to the development of a prototype of a spectrometer with two innovative key features: a circular slit with variable radius and a grating with concentric circular grooves . A certain slit radius identifies a fixed heliocentric height: a radial spectrum of the whole corona at that height is then imaged onto the detector. By changing the slit radius, different heliocentric heights can be explored.
This work presents the prototype design and the status of the project.

We present the most up to date advancements in production, design, and performance of the NexGen Micro-Shutter Array (NGMSA) for Multi-object Spectroscopy (MOS), intended for the future Habitable Worlds Observatory (HWO) Flagship. A microshutter array functions as a programmable slit mask, to generate slits corresponding to sparsely distributed sources in the field of view of a telescope. In contrast to the magnetic/electrostatic microshutter arrays used in the James Webb Space Telescope (JWST), the NGMSA is fully operated by electrostatics, simplifying overall system. Our small pilot array proved its capability from the FORTIS sounding rocket mission in 2019. As we are switching to a larger HWO flight size array process, we are encountering multiple processing related issues. Also, there has been individual shutter level issue that impairs operation and performance. We will discuss those problems and strategies to overcome the challenges to achieve an on/off contrast of >1e5 with near 100% shutter operability.

With the ambitious goal of characterizing nearby Earth-like exoplanets, the Planetary Camera and Spectrograph for the Extremely Large Telescope (ELT-PCS) will need to push the boundaries of both high contrast coronagraphic imaging and integral field spectrograph technology. High contrast imaging spectrographs typically employ microlens array-based integral field units (IFU), which provide a large number of spaxels in exchange for short spectra and an inefficient use of detector pixels. In contrast, image slicers provide a high detector use efficiency with a broader spectral bandpass. We report on the progress of a trade study into IFU design choices for ELT-PCS using a modular integral field spectrograph test-bench. At the core of the experiment are two custom-built IFUs: a novel image slicer-based IFU manufactured by Canon Inc. and BIGRE-like microlens array IFU. We provide an overview of the experiment, the individual performances of the two IFUs, and outline future applications of the test-bench for the design of the integral field spectrograph sub-system of ELT-PCS.

Image slicer technology has undergone great developments in the last decades. Innovative solutions are proposed for the largest night-time and solar telescopes, as well as for space applications. The science cases for the next generation of instruments require pushing image slicer technology beyond its current limits. Future developments are focused mainly in two key parameters: the reduction of the slicer mirror width and the improvement of the surface roughness.

The need for narrower slicer mirrors to achieve higher resolution, better surface roughness to reduce stray light, and innovative ideas for highly efficient Integral Field Spectrographs are investigated in two projects: MINOS and LUCES developed in the UK by a consortium between Durham University and University College London. The main results are presented in this manuscript.

Fiber optic based multi-object spectrographs have been in use for astronomical surveys since the 1980’s. Towards the end of the 1990’s and the early 2000’s the multiplex capability grew to allow hundreds of astronomical targets to be observed simultaneously within the same telescope field of view (e.g. 2dF^[1], Sloan Digital Sky Survey^[2]). Additionally, recent instruments have been developed with considerably higher target counts and with implementation on larger aperture telescopes (LAMOST^[3], HETDEX^[4], DESI^[5], 4MOST^[6], WEAVE^[7], PFS^[8], MUST^[9]. Design studies are currently in progress for more massively multiplexed spectrographs on telescopes with apertures of 10 to 20 meters (MSE^[10], WST^[11], Chinese 12m^[12]) with target counts approaching 20000 and larger. The increasing number of spectrographs needed for these facilities are ever larger in size with correspondingly difficult, risky, and costly designs.

We present a design and laboratory evaluation of a prototype pre-spectrograph wavelength splitter and pupil slicer (WSPS). The goal is to remove the need for the large wavelength splitters that are currently implemented within the multiwavelength channel spectrograph optics and to achieve a more efficient packaging of the resultant single channel spectrographs.

The WSPS is an optical assembly that interfaces to a subset of the incoming fiber optics (~100 per unit), splits the light into multiple wavelength channels (Blue, Green, Red, J, and H), and allows implementation of an arrayed output configuration to slice up the pupil. Performance of the WSPS must achieve excellent light coupling of the incoming light to the output channels and suppress scattered light cross talk so that bright targets illuminating the WSPS don’t contaminate the spectra of the fainter targets that illuminate that same WSPS unit. Nano-structured etching (TelAzTec) is used on the Fused Silica lenses that clad the optical assemblies to suppress optical ghosting.

The TOLIMAN space mission confronts the challenge of detecting Earth analogues in the immediate solar neighbourhood by using novel astrometric techniques. This bespoke, low-cost mission will employ a novel optical and signal encoding system, enabling high-precision measurements that typically require larger instruments. Targeting the Alpha Centauri system, TOLIMAN will utilise an innovative diffractive pupil to mitigate the limitations of a relatively modest satellite and payload infrastructure to make measurements at the extreme precisions required. In this work, we describe the design and manufacturing of the pupil, which employs liquid crystal technologies and substrates with low coefficients of thermal expansion, with the goal of making measurements resistant to inevitable optical distortions and aberrations.

Volume Phase Holographic Gratings (VPHGs) have become a staple of astronomical spectrograph design over the last several decades. VPHGs commonly employ dichromated gelatin (DCG) as the index modulation medium which provides high efficiency, low stray light, robust environmental protection, and high index modulation – thereby enabling wide spectral bandwidths and angular tuning. However, wavefront performance can be a compromising factor in system design, even when gratings are polished after assembly using traditional polishing techniques. The final diffracted wavefront of a DCG-VPHG is a combination of several compounding factors: substrate homogeneity, surface flatness, holographically recorded wavefront, processing techniques, bowing of the glass during the capping process, and imprinted adhesive wavefront errors, some of which can be mitigated through careful process control. To address the remaining gap in wavefront error relative to other components, we propose custom magnetorheological finishing (MRF). In this paper, we demonstrate the wavefront improvement observed by applying custom MRF to a large diffraction grating (15 x 15 cm). The performance enhancements to be shown promise to improve grating wavefront performance considerably, thus improving overall system performance. The grating used in this study is part of a technology demonstration for the future HARMONI Spectrograph for ESO’s Extremely Large Telescope (ELT). The grating for this wavefront improvement project has been produced as a collaboration between University of Oxford researchers, Wasatch Photonics, and QED Technologies.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 470nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. The diffraction gratings are the single biggest contributor to the instrument’s throughput loss. Additionally, the range of operating modes and configurations available to HARMONI users will result in a varying beam footprint at the grating surface. HARMONI’s four spectrographs will be equipped with 10 gratings each, requiring a bespoke automated test facility to qualify the transmission performance of all the HARMONI gratings. This paper describes the test bench, and presents transmission efficiency results for different HARMONI gratings.

Volume Phase Holographic Gratings (VPHGs) have introduced, in recent years, a significant improvement in low and medium resolution spectrographs with an apparent throughput step up. They are still considered the baseline for the DE in low and medium resolution spectrographs. At INAF-Osservatorio Astronomico di Brera, we have been developing VPHGs based on an innovative approach for some years. Almost 15 produced VPHGs are operating in spectroscopic facilities and some prototypes are under production for several spectrographs. VPHGs up to 190 mm in diameter can be manufactured in a wide range of line density. Moreover, innovative configurations, such as multiorder grating and stacked grating, have been developed to increase the spectral range and resolution at the same time. The next steps will be the improvement of the VPHG performances especially in the diffraction efficiency across the bandwidth and the transparency in the UV. Concerning the size of the diffraction elements, a new facility is under building that will be capable to produce VPHGs up to 450 mm in diameter.

Over the past two years, we have been developing the Reactive Ion-PLasma Etched (RIPLE) grating technology. Early on, we demonstrated the process to be a highly predictive, based on experimental verification of the near theoretical super-broadband diffraction efficiency from a proof-of-concept 1x1 sq. inch RIPLE grating. All measured 0^th and 1^st order diffraction efficiency scans from this prototype matched numerical model predictions within 2% at 1σ-level, indicating a highly stable process and non-significant level of defects on the device. The fabrication process was shown to be repeatable over the same area and grating form parameters, and we extended it to larger grating areas with deep-etched grating line features. We demonstrated area scaling to 2x2 sq. inch via an iterative etching technique and recently reached the primary 4x4 sq. inch target. We discuss the evaluation of this area scaling effort.

Bridging the gap between JWST and ALMA, the far-infrared wavelength range between 30 and 300 micron, contains a wealth of spectral features enabling deep studies of galaxy evolution and planet forming systems. One of the key diagnostic tools used by far-IR astronomers is spectroscopy, employing low resolution (R~100) grating modules to achieve the highest possible spectroscopic sensitivity and mapping speed. The next generation of space missions in this field, as exemplified by the Origins Space Telescope (OST), and recently proposed concepts like the PRIMA, FIRSST and SALTUS, will utilize grating spectrometers combined with ultra-sensitive large-format KID detector arrays. Such grating modules will enable a variety of instrument architectures offering powerful observing capabilities including post-dispersed Fourier Transformation Spectrometer (FTS), long-slit spectroscopic mapping, and high-resolution Fabry-Perot or a Virtually Imaged Phased Array (VIPA) based spectroscopy, where the grating is used for order-sorting. To fully exploit the astronomical potential these instruments require compact, cryogenic and wideband grating spectrometers with a large telecentric field of view.

In this paper we present the opto-mechanical design and realization of a multi-purpose Grating Module Breadboard (GMBB), which supports arbitrary one-octave bandwidth diffraction gratings in the 25-400 micron wavelength band. The purpose of realizing this GMBB is to aid experimental verification of blazed grating developments, and to verify the optical interfaces and spectral characteristics of KID detector arrays.

The driving concepts, methodologies, engineering solutions and finally the realization are discussed and supported by optical verification results. A simple and modular configuration containing a collimator unit and camera bay optics allows for easy adaptation to different wavelength/dispersion combinations by exchanging the grating and/or detector array. The opto-mechanical design is monolithic with highly accurate and reproducible kinematic optical mounts, while allowing mirror realization with the highest optical performance. Special attention is given to the development of grating production methods for high-efficiency blazed gratings optimized for specific wavelength bands.

This paper focuses on the development of an essential building block needed to achieve high spectral etendue in integrated optical spectrometers based on Fourier Transform methods: the active phase modulation of the fringes to sample. The long term objectives of this project are to achieve high-resolution spectrometry in a large spectral range, using compact spectrometers based on the SWIFTS (Standing Wave Fourier Transform Spectrometer) approach. The primary applications in astronomy will be precise measurement of atmospheric compositions of detected exoplanets as well as other celestial bodies, such as the detection and analysis of specific gases like carbon dioxide (CO₂) and methane (CH₄) that are linked to life. The proposed on-chip Fourier transform spectrometer (SWIFTS) approach offers several advantages, including high spectral resolution, compact size, and a robust design. However, the principle of sampling in a simple, passive SWIFTS, implies to extract the signal with the spatial frequency of the detector’s pixel pitch. As the pixels’ pitch is typically 10 m, the interferogram is strongly under-sampled, and the resulting spectral range without aliasing is small (typically tens of nm). The work presented in this paper is devoted to increasing the spectral range by temporal multiplexing, achieving on-chip phase modulation thanks to electro-optic properties of Lithium Niobate. By phase shifting the fringes under the sampling centers, we are able to reduce the effective distance between sampled values, therefore increasing the spectral etendue.

After a brief introduction on the SWIFTS principle, we will focus on the electro-optic modulation of the fringes, and show preliminary results that validate the temporal multiplexing approach and discuss further improvements and the range of application of this active phase spectrometer.

The Off-plane Grating Rocket Experiment pathfinder (OGRE-P) payload is a sub-orbital sounding rocket payload designed to obtain the highest resolution soft X-ray spectrum of Capella to date. OGRE was originally designed with a monocrystalline silicon X-ray optic developed by the Next Generation X-ray Optics Group (NGXO) at Goddard Space Flight Center (GSFC). This version of OGRE will be launched in the ultimate OGRE mission, OGRE-U. OGRE-P will use the Joint European X-ray Telescope (JET-X) in place of the GSFC optic in order to achieve an earlier launch date and test other components prior to the ultimate launch. JET-X has an angular resolution of 15 arcsec, which will produce an X-ray spectrum a factor of 3 broader than the GSFC optic. An updated error budget will be presented to reflect the alignment requirements for this lower spectral resolution optic, and the expected achievable resolution will be calculated. A plan for achieving alignment within these new tolerance requirements will be explained.

Silver-based astronomical telescope mirrors (Ag-mirrors) excels in their optical performance across the visible to infrared spectrum. However, without proper safeguarding, they degrade significantly in high temperature/humidity environmental durability tests. Our research explored low-temperature atomic layer deposition (ALD) to prepare a 60 nm aluminum oxide (AlOx) protection coating for Ag-mirrors. We compared two oxygen precursors: water (H2O) and high-purity ozone (PO). PO, with over 80% purity, enables efficient ALD processes at lower temperatures, addressing challenges posed by H2O. During environmental tests, PO samples outperformed H2O samples. PO samples exhibited a minimal reduction (12%) in optical reflectance in comparison to H2O samples that showed substantial reduction (30%). Additionally, PO samples displayed a mere 6 nm phase shift in ellipsometry compared to 74 nm of H2O samples, indicating better structural integrity. Structural analysis revealed that H2O samples experienced erratic changes, compromising integrity, while PO samples maintained their original structure.

Most telescope mirrors of the European ELT shall have protected silver coatings that are highly reflective across all astronomic wavelength bands from the UV (370 nm) to the far infrared. Another aspect is that the coatings shall be frequently cleaned in situ, so they must be highly durable against abrasion and chemical agents such as sulfur and salt. However, they also must be easy to strip with a non-toxic etchant before each recoating. We identify trades and optimize silver coating recipes with different protection layer materials and thicknesses to meet these partly contradictory objectives. A test coating campaign is ongoing.

Advanced telescope mirror coatings have become essential for enabling new and exciting astronomical discoveries. With their ability to maximize reflectivity, reduce scattering, withstand aggressive environments, and optimize specific optical properties, advanced thin film deposition systems help telescopes to see farther and fainter with less light than ever before. This paper discusses various types of film stacks and coating technologies that can be used for demanding coating applications. An overview of challenges with different system configurations will be discussed along with practical solutions to enable uniform, high performance, coatings on large mirrors. The suitability of various mirror coating technologies, such as filament evaporation, electron beam evaporation, and magnetron sputtering, will be discussed and compared for specific mirror coating applications. Hardware design challenges, including source placement, mask and uniformity optimization, and shutter reliability, will be evaluated. Prevalent issues with mirror handling, particles, and long-run reliability will also be discussed in detail.

Large aperture telescope mirrors require reflective films with higher reflectivity to improve their optical efficiency and better stability to maintain their reflective performance. In this paper, an enhanced aluminum reflective film was deposited on a 2.5-meter mirror using ion beam-assisted deposition technology in a 3.2-meter coating equipment. Through the enhancement of the reflective performance of the aluminum reflective film by the dielectric film, the average reflectivity of the aluminum reflective film was improved to 91.3% within the 350-1700 nm wavelength range, and the reflectivity of the three working wavelength bands was increased to 95%. A full-dielectric reflective film was deposited on a 1.7-meter mirror, and the average reflectivity in the full aperture range of 1010-1090 nm was greater than 99.8%. After testing, the reflective mirror coated with the outermost dielectric film exhibited good friction resistance, and the dielectric film itself possessed excellent environmental stability. Applying it to the surface of metal films can effectively reduce the contact between metal films and the external environment, thus slowing down the degradation of the reflective film's performance. Dielectric films can improve the reflectivity of metal films and enhance the overall environmental stability of the reflective film, making them highly suitable for use in large aperture telescope mirrors.

The Instrumentation Division of the Instituto de Astrofísica de Canarias (IAC) is involved since several years in upgrading its capacities to design and manufacture optical components. To this end, we have created a new laboratory (Centre for Advanced Optical Systems, CSOA) which will be capable to design, fabricate and qualify large optical elements. Within these efforts, an optical coating facility is being built aimed at coating and surface finishing of different components, such filters, mirrors and alike, with sizes ranging from few cm to about 1.5 m. The facilities are still in construction and we have already started to experience with medium size filters and mirrors, using a large variety of metallic coatings, both for antireflection properties and spectral band selection.

Our present capacities included a sputtering coating machine, capable to treat pieces up to half a meter of diameter, and E-beam and thermal evaporation. In this contribution we describe the current laboratory setup and report on the results achieved so far in the field of surface coating with different materials.

NASA’s future Habitable Worlds Observatory (HWO) will enable the direct detection and characterization of Earth-like planets around Sun-like stars using high-contrast imaging. One of the most promising approaches to achieve this goal is to use a coronagraph. A good candidate for implementation in HWO is the vortex coronagraph, which is featured in both earlier mission concepts HabEx and LUVOIR. However, HWO would benefit from a scalar vortex coronagraph instead of the well-established vector vortex coronagraphs in order to increase throughput and reach its ambitious goal of characterizing Earth-like exoplanets. Metasurfaces present a promising technology for achromatizing scalar vortex coronagraphs, because they allow for more design freedom in a single layer of constant thickness compared to scalar vortex phase masks based on variable thickness of a dielectric substrate. Here, we present our progress in developing metasurface scalar vortex phase masks. We present updated broadband designs of scalar metasurface phase masks of different topographies (vortex and phase knife), and simulate their performance with appropriate simulation tools. We also discuss first manufacturing attempts at such masks, and outline the next steps needed to push their performance towards the levels required for HWO.

ALD and ALE have emerged as thin-film coating techniques able to address several technical challenges in space instrumentation. This paper will describe recent work that applies these methods to improve the performance and stability of broadband protected-Al coatings, detector-integrated bandpass filter coatings, and narrowband reflective dielectric coatings. Systems that require the use of thin Al films can benefit from ALE methods that can remove the native oxide that would otherwise degrade UV performance. The performance of ALD mirror coatings operating at far UV wavelengths (90–200 nm) is presented in the context of the emerging needs of the Habitable Worlds Observatory. Trends in spatial uniformity are discussed considering the potential requirements of planned coronagraphic instruments. Extension of the same aluminum/fluoride material system to bandpass filters operating in the far UV are also discussed. Finally, we present recent work on new ALD process for high-index materials like LaF3, and present initial results of high-low multilayer stacks which can which can be useful to produce dichroic or narrowband reflective coatings in the UV.

Efficient and uniform Aluminum-based broadband mirrors are essential components for far-ultraviolet (FUV) astronomy. Plasma-enhanced atomic layer deposition (PEALD) is a low temperature, highly conformal coating process that has previously been demonstrated to produce high quality AlF₃ films, although little has been reported on their performance in FUV applications. An ongoing collaboration between the US Naval Research Laboratory (NRL) and NASA Goddard Space Flight Center (GSFC) focuses on optimizing material properties of PEALD AlF₃ coatings on Al mirrors to enhance FUV optical performance.

PEALD AlF₃ films were deposited using trimethylaluminum and SF₆ plasma precursors in a modified Veeco Fiji G2 reactor. ALD growth windows (the range of process parameters resulting in ideal growth) were established using an in situ ellipsometer to monitor the fluoride growth rate directly on Al substrates and supplemented with post-deposition x-ray photoelectron spectroscopy to elucidate process-structure property relationships. Optimal AlF₃ films had a growth rate of 0.75-0.8Å/cycle, F/Al ratio of ≈3, < 2 at% O, indicating that PEALD is a beneficial process technique towards achieving optical coatings on a variety of potential mirror materials. The influence of PEALD parameters on the FUV optical performance of Al mirrors overcoated with PEALD-AlF₃ will be also discussed.

We designed and manufactured an optical bench to characterize the EUCLID dichroic reflected wavefront at all useful incidences, all polarization states and each wavelength from 550nm to 950nm. The multilayer coating adds indeed some phase effect that vary suddenly in function of the wavelength. The testbed architecture, main functionalities and performances are presented. The preliminary results obtained on the dichroic mirror are compared to some simulations based on an up-to-date model of the multilayer coating.

The Habitable Worlds Observatory (HWO) concept NASA flagship mission aims extend the ultraviolet (UV) observation range and sensitivity capabilities of the Hubble Space Telescope (HST) with respective goals of reaching photons down to 100 nm and containing an ultraviolet multi-object spectrograph with sensitivity improved 30-100 times. Adding the sensitivity capabilities near the Lyman series spectral range of ~100-121.6 nm reduces the reliance of redshift for key diagnostic ion lines such as O VI (103.2 nm), and heavily ionized gases of Ne VIII (77.5 nm) and MgX (62.5 nm). Clean and unoxidized aluminum (Al) reflectors provide optimal efficiency over a broadband down to the extreme ultraviolet (EUV) wavelength of ~83 nm. To prevent oxidation and maintain high spectral efficiency down to ~100 nm, the Al reflector is conventionally overcoated with a thin lithium fluoride (LiF) layer. We investigate the optimization of the deposition of the Al+LiF coating material composition to attain high spectral efficiency broadband reflectors down to 100 nm and enable the scientific goals of HWO. Lithium hexafluoroaluminate (Li₃AlF₆) is investigated as a different composition form of LiF to overcoat Al. The spectral efficiency and durability of the reflectors is evaluated. We will demonstrate the use of Li₃AlF₆ as an overcoat to protect aluminum yields ultra-high efficiency at the Hydrogen Lyman-alpha (HLyα, 121.6 nm) line with experimental reflectance values peaking up to 99%.

The GMT-Consortium Large Earth Finder (G-CLEF) is a spectrograph, to be delivered as the first light scientific instrument for the Giant Magellan Telescope (GMT), and divided into a red and a blue channel.
In the frame of this project, Bertin Winlight is in charge of the manufacturing of the blue camera lenses, and entrusted CILAS to develop and realize the antireflection coatings on the 8 different lenses of this camera. The camera consist of 8 lenses with diameter in the 190 – 323 mm range made of CaF2 and other optical glass (BAL35Y, PBM18Y, BSM51Y). We present the results on the design, development and manufacturing of antireflection coating with PIAD (Plasma-Ion Assisted Deposition) technology, which is well adapted to produce very dense layers and high quality coatings for severe environments.
The design of antireflection coating, in the spectral range 350-541nm, has taken into account large diameter and high curvature of the lenses and has been experimentally validated on a dummy shape. Moreover a dedicated coating process has been implemented and qualified on CaF2 substrates, leading to the successful coating of the 8 different lenses.

Concepts for the next generation of spectroscopic survey facilities (e.g., WST, MSE, MegaMapper) require a fibre-fed multi-object multiplex of ~20,000 in a focal surface area with a diameter of order 1.0–1.5 metres. This puts extreme requirements on e.g., pitch between positioners, collision avoidance, and mass producibility that are hard to meet with current concepts. We present the new FLEX1 fibre positioner concept inspired by mechanisms used for minimally invasive surgery. The concept consists of a parallel mechanism that can be mass produced with laser cutting techniques and a tripod actuator mechanism for accomplishing both positioning and maintaining focus. Advantages of the new design compared to existing positioner designs include very large patrol diameter per fibre (>30 mm) while allowing for very small pitch (~7 mm), very small minimal approaches between fibres, good clustering capabilities (20 fibres can reach a given sky location), easy control path and collision avoidance, robustness, mass producibility, the ability to accommodate nontelecentric and low-order polynomial focal surfaces, and the minimal bending and twisting of the fibre. The mechanism is expected to be very robust and mass producible. While conceived for small pitch, high density applications, the principle can easily be scaled up for larger plate scale for more sparse pick-ups in ELT instruments. A few concept designs of possible implementations are presented together with further development plans.

This paper presents the performances of recent high-tech hexapod positioning systems. Those devices with six degrees of freedom, are commonly used in Ground System Equipment (GSE) design, to qualify and conduct, for example, optical performance test activities. They are frequently used in vacuum environments. This is the case for example for EUCLID, CHIME, PLATO missions. They are also commonly used on large scientific instruments like Telescope or synchrotrons.

The latest innovations in terms of the performances, measurement technology, stability and control of those positioners are presented. The know-how the manufacturer has mastered to mature this technology and push the boundaries is on display. The characterization of the performance in terms of resolution, repeatability, accuracy, cross-coupling, backlash, and stiffness is clarified. The methods and measurement instruments used to characterize each specification are explained. Then, the most advanced performances of different hexapod positioners are described in detail. The goal of this step is to provide the current state of the art of hexapod technology and describe the most advanced system. Ongoing innovations that could push the boundaries are also featured.

Finally, we present how engineers can specify their positioners to be integrated into the next generation of Ground Support Equipment (GSE). This analysis will include key parameters such as the stiffness, duty cycle, thermal management but also the control requirements.

The use of flexures to achieve fibre positioner motion is being actively investigated by several institutes, for example at the UK Astronomy Technology Centre (UKATC) and Leibniz-Institute for Astrophysics Potsdam [1]. One challenge when designing with flexures is the large number of degrees of freedom available which makes it difficult or impossible to optimise their motion by hand.

In this paper we demonstrate two approaches for optimising flexure geometry to follow arbitrary focal surface curvature and to orient the optical fibre with arbitrary tilt. These approaches are: analytical using MATLAB models and FEA based using Ansys. The approaches are complementary allowing the designer to efficiently explore the parameter space and then do precise optimisation of the flexure geometry. We demonstrate the applicability both to the UKATC’s preferred design for WST, and to flexure-based fibre positioner designs generally. We also present a sensitivity analysis relating small changes in design parameters to changes in fibre tip motion. Finally we briefly present the UKATC's preferred geometry for the WST fibre positioner.

The fiber positioner robot is the most crucial actuator in the focal positioning system of a Multi-Object Spectrographs. The double-rotation form of fiber positioner was first extensively used in the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) in 2012. However, as multi-spectral telescopes continue to develop, there is a growing demand for smaller and lighter fiber positioners. Current focal positioning systems are now considering the use of 4 mm motors, which are smaller than stepper motors. However, these motors do not come with a position sensor solution. Researchers have developed a miniaturized position sensor solution compatible with this motor, and it is installed in the center arm of the fiber positioner. Prototypes have been fabricated and, in conjunction with relevant experiments, this paper provides a detailed introduction to the specific impact this angle sensor has on the fiber positioner.

Every photon of light is precious for astronomical observation. Light losses within telescope guiding systems and or losses via poor fiber coupling are common despite advances in photonic technologies in other industries. At CREOL, we develop a fiber feed assembly and alignment method which minimizes vignetting, light losses, optimizes fiber coupling, and optimizes signal-to-noise within our different COTS telescope guiding systems during astronomical observations. We can apply our techniques to the PolyOculus case and single-unit We present our lithographic etching process, each variation of mechanical and optical alignment processes, the final coupling and assembly process, and how the assembly is integrated into a larger acquisition and guiding system for COTS telescopes.

The demand for optical fibre connectors, which offer high throughput, outstanding reliability, and minimal Focal Ratio Degradation (FRD) has become critical in the era of large telescopes where science productivity could be enhanced if focal plane fibres and fibre bundles had the flexibility to be reconnected to feed to any of the instrument suite or for instrument changes. At Astralis we are investigating if it will be physically possible to develop a fibre connector with the ability to connect any fibre pairs without a difference in throughput at a 1% (aim, 2% requirement) level, which has not previously been possible, and is very challenging. The initial stages of this work have been focused on analysis of the best-performing existing connector with the goal of identifying areas where connector (and mating adapters) improvements are most needed. From that analysis, the main causes of FRD and throughput loss have been identified. New connectors are being prototyped to improve the fibre alignment, FRD from both the connector holes, expansion of materials and fibre pressures. In addition, we investigate alternative coupling methods, including dry coupling and the application of index matching gels. We present our findings on the performance of the existing connectors in terms of fibre throughput and FRD in both the optical (370-1000 nm) and near-infrared (1000-2200 nm) wavelength regions. The key design considerations for the next prototype connectors are discussed.

Photonic platforms and technologies can facilitate the miniaturization of astronomical instruments for high-resolution cross-correlation spectroscopy. Fibre Brag grating (FBG) arrays, inscribed into optical fibres using direct femtosecond laser writing, form a target-tailored instrument spectrum. Flexible modulation of spectral features is provided during instrument operation through strain tuning of the FBG arrays. This paper presents a prototype of an astrophotonic fibre instrument demonstrating cross-correlation spectroscopy for molecular gas absorption in the infrared spectrum. Experimental laboratory results of spectral modulation and cross-correlation analysis are shown to compare well with theoretical models for CO2 gas. Additionally, efforts toward the on-sky integration of the instrument on a 1-meter-class telescope are demonstrated for targeted near-infrared spectral features.

We present the design of an athermal package for fiber Bragg grating (FBG) filters fabricated at our Institute for use in ground-based near-infrared (NIR) telescopes. Aperiodic multichannel FBG fibers combined with photonic lanterns can effectively filter out extremely bright atmospheric hydroxyl (OH) emission lines that severely hinder ground-based NIR observations. While FBGs have the capability of filtering specific wavelengths with high precision, due to their sensitivity to temperature variations, the success in their performance as OH suppression filters depends on a suitable athermal package that can maintain the deviations of the FBG wavelengths from that of the OH emission lines within sub-picometer accuracy over a temperature range of about 40K (i.e. 263K to 303 K). We aim to develop an athermal package over the aforementioned temperature range for an optical fiber consisting of multichannel FBGs for a maximum filter length of 110 mm. In this work, we demonstrate the complete design methodology of such a package. First, we developed a custom-built test rig to study a wide range of critical physical properties of the fiber, such as strain and temperature sensitivities, elastic modulus, optimum fiber pre-tension, and adhesion performance. Next, we used these data to confirm the athermal response of an FBG bonded on the test rig from room temperature to 313 K. Based on this study, we developed a computer-aided design (CAD) model of the package and analyzed its athermal characteristics with a suitable selection of materials and their nominal dimensions using finite element analysis (FEA). We finally discuss the novel aspects of the design to achieve high-precision thermal stabilization of these filters in the temperature range of interest. Our design is scalable to longer filter lengths and can also be used for other in-fiber devices for example, FBG-based frequency combs for their stable operations in astronomical applications.

Optical fibers are widely used in ground-based astrophysics, especially in the visible and near-infrared regimes. The use of fibers in other spectral regimes (such as the ultraviolet) and in the space environment has been limited due to the high absorption of most glasses in the UV and the radiation-induced degradation of glasses, respectively. Recently, we have demonstrated hollow-core optical fibers that transmit wavelengths as short as approximately 140 nm. Because oxygen and water vapor strongly absorb light with wavelengths shorter than 180 nm, we performed our transmission measurements in a chamber filled with high purity nitrogen. The fibers we measured show high transmission and low bend-induced losses in the 140 - 250 nm regime. Most recently, we have developed a vacuum system, capable of transmission measurements across the full FUV range (100 - 200 nm). Here, we present fiber transmission measurements in the 115 - 250 nm range and introduce some instrument concepts that are made possible by these FUV fibers.

This work aims to present the first results towards a mid-infrared (L-band : 3.4 μm - 4.1 μm) high resolution integrated spectrometer, based on the Gabor approach of SWIFTS (Stationary Wave Integrated Fourier Transform Spectrometer). In this configuration, a stationary wave is obtained by injecting the light from the source on both sides of a channel waveguide. The centre of the coherent interferogram is obtained in the middle of the waveguide, allowing for full characterisation of the source, and all differential dispersion effects between the two optical paths. The stationary wave is sampled by nano-scattering centres (= nanogrooves) placed on top of the waveguide. They extract the interferogram, and the spectrum of the source is retrieved through a Fourier Transform. In the mid-infrared, the detection area of the detectors is buried : using only one groove per scattering centre leads to a diffracted signal too wide and causes pixel crosstalk. Several grooves per scattering centres have therefore been implemented, as this configuration creates a small diffraction grating, and reduces the angular divergence of the flux. In addition to avoiding crosstalk, this allows to extract more flux per scattering centre, thus increasing the signal to noise ratio. Our samples are made in Lithium Niobate (LiNbO3), an electro-optic crystal, using two technologies. First, Direct Laser Writing for both the waveguides and the nanogrooves, and secondly Titane diffusion for the waveguides and Focused Ion Beam for the nanogrooves. Because of the electrooptic properties of Lithium Niobate, applying an electric field ramp modulation will change the refractive index of the material, allowing to finely scan the fringe packet under the sampling centres, thus increasing the sampling rate of the interferogram by temporal multiplexing. We demonstrate that our waveguides are fully functional and have a correct transmission rate, and that our antennas are extracting the stationary wave as expected, in both technologies.

High-precision timing is vital in space communication for tasks like navigation, data transfer, and coordinating satellite constellations. Currently, ground segments rely on microwave clocks, but emerging optical clocks and links offer great improvements in resolution, precision, and stability for next generation systems. However, integrating optical clocks with conventional microwave sources presents a challenge. Our solution, an optical-to-microwave phase detector, addresses this by enabling synchronization with few-femtosecond residual jitter between an optical- and a microwave source. With a phase/timing resolution of 0.01 fs RMS and a noise-floor below 1 fs RMS, this detector becomes a key technology as optical clock adoption grows in ground segments.

Nulling interferometry has emerged as a promising technique for imaging exoplanets, effectively overcoming the challenges of contrast and angular resolution faced by ground-based telescopes. The Guided Light Interferometric Nulling Technology (GLINT) instrument at the Subaru telescope in Hawaii utilises this technique, where a new integrated optics beam combiner will be deployed, capable of simultaneously performing nulling interferometry and fringe tracking. Fabricated using the femtosecond laser direct write technique in boro-aluminosilicate glass, the beam combiner integrates three single-mode waveguides as inputs to form 3 interferometric baselines. The design, fabrication and laboratory characterisation of the new beam combiner will be presented. The beam combiner comprises of 3D-printed micro lenses, a chrome mask, Y-Junctions, achromatic phase shifters and tricouplers to produce for each baseline an achromatically-nulled and two phase-sensitive bright outputs. This results in a total of 12 outputs that are directed onto a CRED2 camera.

The characterization of exoplanets is critical to understanding planet formation, and the search for life. To directly characterize Earth-like exoplanets, a contrast ratio of 10⁻¹⁰ between the star and planet must be overcome. The GLINT instrument is an integrated photonic nulling interferometer fabricated using ultrafast laser inscription, where all routing, beam splitting, phase shifting and recombination is done within a single photonic chip. The instrument uses pupil sub-aperture’s to create different baselines. An achromatic π phase shift is then applied to baseline pairs and recombined in a tricoupler. This suppresses the on-axis starlight while off-axis planet light is observed in the “null” output. The Achromatic phase shifters are designed using differential waveguide dispersion where lengths of three different widths combinations are used to create a differential achromatic phase shift. Adiabatic tapers are then used to transition between regions of different widths to reduce losses. Using this method, a 3.6 mm long 180° achromatic phase shifter was fabricated, and measured to have a phase shift of 171.5 ± 4° from 1440-1640 nm. This phase shift is comparable to GRAVITYs 90° phase shifters (85 ± 3°).

Optical fiber spectroscopy technology is widely used in astronomical surveys. Due to the flexibility and long-distance transmission characteristics of the fiber, astronomical observation can gain larger scale and higher precision spectral data. Nowadays, a lot of representative technologies have been presented to enhance spectral resolution, including fiber integral field spectroscopy, fiber positioning technology in the sky survey, adaptive optics, and photonic lantern technology. Fiber spectroscopy technology plays a crucial role in astronomy. The long-distance transmission characteristics of fibers separate the telescope from the spectrograph. The intrinsic flexibility of fibers lends itself readily to reconfigurable sampling of the field. The method to improve the spectral resolution has been gradually proposed. Fiber integral field spectroscopy is one of the most typical techniques to enhance the spectrum resolution. The flexible combination of fiber bundle and microlens is used to improve the sampling rate of target stars and fitting factor. In the observation of target stars by a single fiber, the alignment accuracy between the fiber and the star image determines the spectrum resolution. In the multi-object telescope, the position of a large number of multi-mode fibers needs to be detected. As a kind of optical waveguide device with multi-mode and single-mode conversion, photonic lantern can convert the energy collected by multi-mode fiber into the output of single-mode fiber. This review introduces optical fiber technology on astronomical observation.

The PLACID instrument installed at the new Turkish 4m-DAG telescope in 2024 will be the first active stellar coronagraph, offering a unique facility to perform innovative high-contrast imaging observing strategies. It is composed of a Spatial Light Modulator (SLM) in reflection in lieu of the usual fixed focal plane mask to digitally set up any phase mask in real time. However, such hardware works with a linearly polarized wave causing the loss of 50% throughput. To retrieve full capacity, PLACID will then be upgraded with polarization-independent solutions to be first tested on the Swiss Wideband Active Testbed for Coronagraphic High-contrast imaging (SWATCHi) 2.0. This testbed is also employed to investigate coherent differential imaging techniques that relies on the fast modulation of the speckle intensity whose signal is recorded with a C-RED ONE camera. This work presents the optical design and first results of SWATCHi 2.0.

The Mid-Infrared ELT Imager and Spectrograph (METIS) is one of the three first-generation instruments of the Extremely Large Telescope (ELT). METIS will enable high-contrast imaging through different coronagraphic modes, one of which is implemented with a vortex coronagraph. However, the complex pupil of the ELT with its large central obscuration limits the performance of a classical vortex coronagraph. Using a grayscale ring apodizer in a pupil plane upstream of the vortex phase mask can correct for the effect of the central obscuration and partly restore the coronagraphic performance of the vortex for the ELT pupil. The coronagraphic performance of the ring-apodized vortex coronagraph relies on the precise control of transmission in the grayscale region, which can be implemented using a technology based on chromium microdots. Here, we present the ring apodizer for the METIS instrument exploiting the microdots technology. We first describe the design process of microdot patterns and perform simulations for both transmission and phase response of the microdots with various geometric parameters. We then describe the manufacturing of three prototypes featuring different design parameters, as well as their testing in terms of transmission and phase response. Finally, capitalizing on the lessons learned, we report on the current status of manufacturing and testing of the final ring apodizer for METIS.

Visible light high-contrast imaging is exciting because of the possibility to detect accretion tracers like Hα at extremely small separations, but this is complicated by high atmospheric turbulence. To overcome this limit, AO188 is being upgraded and SCExAO/VAMPIRES has received more sensitive cameras and a multi-band imaging mode. To take advantage of these upgrades, a high-performance broadband coronagraph is needed. In this paper, we report on the installation of a liquid-crystal double-grating vector-vortex coronagraph with these properties in October 2023. We detail the high-quality manufacturing of the mask by Colorlink Japan, ltd and show its performance characterization with an internal source and on-sky using the multi-band imaging mode, simultaneously imaging four wavelength bands. We describe our efforts to calibrate the mask for polarimetry, review possibilities for an upgrade for simultaneous multi-band focal-plane wavefront sensing, and discuss the performance in the context of the balloon-borne PICTURE-D mission and future space missions.

High-contrast imaging instruments use coronagraphs for studying stellar environments by suppressing the intense glare of stars. The Annular Groove Phase Mask (AGPM), a vector vortex coronagraph, has proven to be a valuable tool, offering high-contrast performance at small angular separations. The Mid-infrared ELT Imager and Spectrograph (METIS) project will incorporate multiple AGPMs designed to operate at various wavelengths within the LMN spectral bands. Recently, the METIS project has entered the Manufacture, Assembly, Integration, and Test (MAIT) phase. During MAIT, the AGPMs, referred to as Vortex Phase Masks (VPMs) in the framework of METIS, are subject to an iterative process of manufacturing and testing. In the event of performance discrepancies, a component undergoes a minor re-etching process and is subsequently re-tested until it meets the specified requirements. In this work, we evaluate the performance of the METIS VPMs on two distinct coronagraphic test benches. On one hand, the Vortex Optical Demonstrator for Coronagraphic Applications (VODCA) at the University of Liège, featuring a supercontinuum laser source and a FLIR infrared camera, is employed to assess the METIS L- and M-band VPMs. On the other hand, the performance of the METIS N-band VPMs is assessed using a cryogenic testbed at CEA Paris-Saclay. This second testbed is equipped with a series of lasers spanning the 8 to 12.5μm range, ensuring high wavefront quality with a single-mode output. We present the outcome of our extensive manufacturing and testing campaigns and reveal the measured coronagraphic performance results for all METIS VPMs.

The Evanescent Wave Coronagraph uses a focal plane mask comprising a lens and a prism placed in contact so that frustrated total internal reflection can occur - the principle governing starlight attenuation. This type of Lyot coronagraph has three main capabilities: i) the mask adapts itself to the wavelength, ii) the size of the mask is adjustable by pressure adjustment, and iii) both the light coming from the star and companion can be collected simultaneously. Previous experimental results, obtained without adaptive optics and in unpolarized light, showed a raw contrast of 10⁻⁴ at 3 λ/D in the I-band and at 4 λ/D in the R-band. Its performance has been limited so far by uncorrected residual aberrations of the optical bench that generate speckles close to the inner working angle. To study the mask performances close to the diffraction limit and compare them with theoretical models, a deformable mirror is installed in the optical path of the testbed to perform wavefront correction. In this work, we report the results obtained in the laboratory using this upgraded setup. We show the preliminary results of correcting the non-common path aberrations using the scientific camera as the wavefront sensor and compare them with expected theoretical performances. The corrections are applied after finding the optimal commands that maximize the variance at the detector plane.

The objective of the coronagraphic IFU of RISTRETTO is to enable High Dispersion Coronagraphy of planets at a distance of 2λ/D from their star, without compromising on transmission. The new idea of a PIAA Nuller (PIAAN) allows contrast down to 10⁻⁵ over large bandwidth ≥ 25%, with high transmission ≥ 70% at the distance of 2λ/D. While RISTRETTO will be installed on a VLT, this development is of tremendous importance for fully exploiting future ELTs XAO. We will discuss our PIAAN prototyping activities. This covers 1) the characterisation of our 2nd set of IFU bundles, with 3D-printed MLAs; 2) the characterisation of our first PIAA optics; 3) the integration of a high contrast bench, planned for prototyping of Front-End control strategies; 4) the characterisation of the PIAAN system on the bench.

Presently, the field of astronomy is transitioning towards the analysis of extensive datasets and all-encompassing sky surveys, moving away from the traditional study of individual celestial bodies. The imaging terminal of large field of view sky survey telescopes is typically equipped with a splicing camera consisting of CCD/COMS detectors. In order to enhance the signal-to-noise ratio of imaging and mitigate dark current, the splicing CCD imaging surface must be enclosed within a vacuum Dewar and cooled to temperatures ranging from -80 to -100 ℃. This poses a significant challenge in facilitating the electrical signal feeding and readout of multiple detectors within a low-temperature vacuum environment. This study employs glass sintering and bonding techniques in conjunction with thermodynamic simulation analysis to achieve the transmission of more than 1600 signals through a constrained flange surface. Environmental adaptability is maintained through the thermal matching of materials, and the introduction of a stress relief groove mitigates the impact of flange surface deformation on bonding positions under vacuum conditions. Following multiple rounds of temperature loop test, it was determined that the leakage rate of the vacuum feedthrough component can be controlled to ≤ 1E-9 Pa • m ³/s. The high-density signal vacuum penetration scheme proposed in this study holds important implications for the design and signal extraction processes of multi-detector splicing focal plane cameras.

The FIRSST (Far-Infrared Spectroscopy Space Telescope) identifies the physical processes of planets formation, traces the flow of water, witnesses the galaxy growth to cosmological distances. The payload consists of a primary telescope and two instruments spanning tens to hundreds of micron wavelengths provide low to super high spectral resolving power. One instrument is cooled to 120 mK with a flight heritage ADR design. The other instrument detector, the heat sink for the ADR, and the entire telescope are cooled to 4.5 K with the Ball 4 K Cryocooler. The passive thermal system significantly reduces the cooling requirement for the 4 K Cryocooler. The multiple thermal stage architecture provides thermal immunity to the thermal environment load. FIRSST’s cryogenic thermal system meets all thermal requirements with margin. Ball’s experienced design team leverages lessons learned from past programs, included verification testing throughout all program stages, ensuring all thermal requirements are met with margin.

In cryogenics, working together with cryocoolers, the thermal straps are a critical thermal element, since they thermally link the instrument with the cold source. In optical elements that work at cryogenic temperatures, the thermal path, and therefore the straps, must isolate them from the vibrations of the cryocoolers. Consequently, its stiffness is a characteristic to consider in the design. But, in the case of optical focal plane arrays, working at very low temperatures such as 50 mK, it can be resonant with the low frequency range of the cryocoolers, and its dissipation can break the superconducting state of the sensors, the basis of its functioning. It is therefore an undesired thermal effect derived from structural behavior. Design limitations impose the need for straps where stiffness is just as important as its conductance. The stiffness value needed is much lower than the one found in commercial straps. Therefore, this work highlights the design, and characterization tests of different strap prototypes in order to achieve the necessary resistivity and thermal conductivity for low cryogenic temperatures. The thermal straps were initially designed for the Cryostat facility for 2K Core Calibration (C2CC) a ground equipment for the ATHENA project (Advanced Telescope for High - ENergy Astrophysics, ESA).

The Camera Head of the Wide Field Imager (WFI), which is to fly on the X-ray telescope NewAthena, is a compact sub-system requiring the integration of three separate temperature regions. One will be the environment temperature of the instruments support structure. The other two temperature environments are governed by the requirements of the detector front-end electronics and the sensor itself. Due to the limited space available and high heat fluxes that the system needs to remove at temperatures as low as 160 K, graphene thermal straps are used. Although already in use in some space applications, space qualified graphene thermal straps are not available on the market, therefore a qualification program, specific for the environmental conditions and requirements of the WFI system, has been carried out. The thermal straps are tested for their thermal performance, structural stability and particle shedding, thermally cycled and outgassed.

This paper presents the design and technical progress of a precision X-Y stage for detector dithering and flexure compensation being developed for the Magellan InfraRed Multi-Object Spectrograph, MIRMOS. Designed to operate at 80 K, the stage will accurately control detector position in two orthogonal degrees of freedom. The piezo-driven flexure stage is very compact providing high-resolution backlash-free motion of the detector. A magneto resistive bridge provides position feedback in each degree of freedom, greatly reducing hysteresis, which is common in piezoelectric actuators. The system is designed to operate in open loop using a lookup table keyed to the Nasmyth rotator angle for flexure control. Here, the optomechanical design of the stage, electrical control system, and performance results from early prototype efforts are presented and discussed.

The National Aeronautics and Space Administration’s (NASA) Astrophysics Division (APD) funds the development of cutting-edge technologies through multiple programs to enable its strategic missions to achieve ambitious and groundbreaking science goals. These technology development efforts are managed by the Cosmic Origins (COR), Exoplanet Exploration (ExE), and Physics of the Cosmos (PhysCOS) programs. The 2020 Astronomy and Astrophysics Decadal Survey, “Pathways to Discovery in Astronomy and Astrophysics for the 2020s” [1] (Astro2020), recommended a pan-chromatic set of missions, including three Great Observatories (GOs) and three Probe-class missions that could collect unprecedented data over the coming decades. We show the correlation between these strategic missions and the current astrophysics technology gaps, as well as recent and current technology maturation projects funded to help close these technology gaps. We also cover how these investments advanced their Technology Readiness Levels (TRLs) [2] and where they have been infused into missions and projects.

The European Southern Observatory (ESO) is at present constructing the Extremely Large Telescope (ELT), a 40-m class astronomical telescope on top of the 3046 m high mountain Cerro Armazones in the central part of Chile’s Atacama Desert. In combination with its powerful facility instruments, it will be the largest optical/near-infrared telescope in the world, also known as the biggest eye on the sky. The instrument roadmap lists up to eight scientific instruments, whereof the first light instruments were already completing their final design phase. Nowadays massive instruments, each weighing about 20 to 40 tons, are requiring powerful cryogenic systems for cooling the cold mass of several tons of each individual instrument.

The paper outlines the cryogenic requirements defined by the ELT instrument suite and describes concept and design of the cryogenic infrastructure. A centralized and fully automated system combining open loop Liquid Nitrogen cooling in combination with low-vibration mechanical cryo-coolers is the baseline for providing the required cooling capacity and temperature levels as low as 4 Kelvin. Project status and timeline are presented.

The Mid-infrared ELT Imager and Spectrograph (METIS) is one of the scientific instruments for the ELT. The Common Fore Optics (CFO) is the first set of optics and mechanisms within the cryogenic instrument. A key element of the CFO is the Pupil Stabilization Mechanism (PSM), a tip/tilt mirror used for periodic adjustments of the pupil alignment during observations. The design challenges for the PSM involved achieving the required stability, resolution, and a sufficient stroke range/hold power while operating within the stringent requirements of the CFO. The design development lead to a monolithic design and integrated flexures driven by actuators with an integrated closed loop optical encoder.

This paper describes the work performed by the CEA Paris-Saclay team to build and qualify a cryogenic derotator mechanism for the ELT-METIS instrument. As the Extremely Large Telescope is an azimuthal telescope, a field derotator device is mandatory to keep the sky image perfectly aligned on the detector frame during the observations. The METIS consortium has chosen to place the derotator mechanism inside the cryogenic vessel, operating at 70 K under vacuum to reduce the background noise at the lowest level. This article gives the main results of the achieved performances, including a positioning accuracy in the arc second range.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 470nm to 2450nm with resolving powers from 3300 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews.

The core of HARMONI is the Integral Field Spectrograph (IFS) which is composed of different subsystems including the IFS Pre-Optics (IPO). The IPO main objective is to take light from the focal plane relay system and reformat and condition it to be a suitable input for the rest of the instrument. The IPO in HARMONI includes the IFS Pre-Optics Fast Shutter (POFS), a mechanical cryogenic fast shutter which will be used with both the visible and infrared detectors. This mechanism has been designed to be fast and reliable and its design has already passed the Critical Design Review (CDR) but specific issues that require further analysis have been identified. The functioning of this element is a critical part in HARMONI and, consequently, a prototype has been used to analyze possible improvements in the CDR design and to perform extensive testing before the Final Design Review (FDR).

In this work we present the design of the IFS Pre-Optics Fast Shutter and the test results obtained with the prototype developed at the facilities of the Instituto de Astrofísica de Canarias (IAC).

HARMONI is the high angular resolution optical and near-IR integral field spectrograph for the Extremely Large telescope (ELT). It covers a large spectral range from 470nm to 2450nm with resolving powers from 3300 to 18000 and spatial sampling from 60mas to 4mas. The Instrument Pre-Optics (IPO), a sub-system under the responsibility of the Instituto de Astrofísica de Canarias (IAC), consists of several opto-mechanical mounts operating at cryogenic temperatures. Among these, toroidal mirrors stand out as the most sensitive and accurate elements of the IPO. An athermal design has been achieved by combining different materials for both the mount and the pads that define the position of the optical element. This design compensates the differential contractions during cooling, which allows the optical element alignment to be maintained within the tight tolerance when transitioning from warm to cryogenic operating temperatures. This paper presents the design of the athermal toroidal mirror mount, the tests carried out on its prototype and the final optomechanical mount.

MICADO is a first-generation instrument for the ELT. It will provide diffraction-limited imaging in standard, astrometric, and coronagraphic modes and long-slit spectroscopy at near-infrared wavelengths. The core of the MICADO instrument is its cryostat, which cools the internal optical and mechanical subsystems to 80 K. Following a light ray entering the cryostat through the entrance window, the first mechanism it encounters is the Focal Plane Mechanism. It consists of two independent movable devices mounted in one assembly: the aperture wheel and the focal plane wheel. The primary purpose of the aperture wheel is to rapidly block the light path, which is needed to mitigate persistence on the detectors. The focal plane wheel holds field stops, calibration masks, slits, and coronagraphs. The positioning requirements for the wheel are dominated by the coronographic masks demanding a 15 μm RMS repeatability. To fulfill this specification and avoid mechanical wear in the drive, a novel magnetically coupled gear system was developed at the Max Planck Institute for Extraterrestrial Physics (MPE). A magnetically coupled worm gear uses magnetic forces to transmit torque from the motor to the driven component without direct mechanical contact. This paper describes the design and performance of the magnetic drive and the first results of the focal plane wheel prototype tests in a cryogenic environment.

The Detector Positioning System (DPS) is a cryogenic mechanism operating at 82 K installed in the cryostat of the Multi- AO Imaging Camera for Deep Observations (MICADO) at the Extremely Large Telescope (ELT).
The DPS mechanism will be exclusively utilized during the alignment and test phase. Upon completing the test phase, it will be mechanically locked at the best pre-determined focus so that it cannot be moved during the observation period.
The DPS has been conceptualized as a fixed and reproducible interface to the Main Bench Structure in the MICADO cryostat and as an adjustable unit containing the Detector Array mounted on the DPS frame installed on a linear guide on the base plate. A cryogenic linear actuator further acts as the linear guide during the alignment phase to bring the focal plane array into focus.

Astronomy and Space Domain Awareness are limited by the size of available telescope optics, the cost for which scales steeply due to the exquisitely ground and polished primary mirrors, typically made of glass or other light-weight substrates. Liquid mirrors (LMs) may break this unfavorable cost scaling. When rotated at a constant angular velocity, it has been shown that fluid surfaces take the form of a paraboloid, which can function as a primary mirror. However, current LMs cannot slew or tilt off-zenith due to gravity, greatly limiting the viewing area in the sky. To overcome these limitations while also enabling low-cost, very-large-aperture telescopes, DARPA launched the Zenith program. Zenith is developing entirely new LM design-for-build approaches that can create large optical surfaces and maintain optical quality during tilt and slew by correcting transient liquid surface aberrations in real time. The development of these new designs is being supported by multi-physics models, materials, surface and field controls, and structures. This paper discusses key and fundamental aspects of four new design and modeling approaches for this new class of LMs. The software and simulation tools developed by the Zenith program to design tiltable and size-scalable liquid mirrors are also available to the astronomical community as an open-source repository.

We present experiments performed in parabolic flights and in space, demonstrating the use of Fluidic Shaping to create optical components in microgravity. By injecting optical liquid into a circular bounding frame in microgravity, surface tension drives the liquid to a minimum energy form of a spherical lens with sub-nanometric surface roughness. We will discuss the engineering challenges encountered in such experiments, and provide details and insights towards the future implementation of similar experiments in microgravity. We view this set of experiments as the first milestones in expanding in-space manufacturing capabilities to also include optical components. Due to its simplicity, low power consumption and essentially zero waste, Fluidic Shaping can serve as a fabrication infrastructure for future long-duration space missions that must be self-sufficient. Due to its scale invariance, the method could potentially be used for the creation of large space telescopes, thus overcoming launch constraints.

As a collaborative effort within the Thirty Meter Telescope (TMT) project, India is committed to supplying 84 polished segments for the primary mirror, employing the innovative Stressed Mirror Polishing (SMP) technology obtained from Coherent Inc., USA. SMP allows for the efficient polishing of highly aspheric non-axisymmetrical glass blanks at an accelerated rate. India-TMT (I-TMT) successfully applied SMP to qualify three glass roundels at Coherent's facility in Richmond, CA. The study focuses on a comparative analysis of Buyoff Stations (BOS) used in the SMP process. It contrasts results from the 43-point hydraulic-based BOS at Coherent with simulated outcomes from the 27-point whiffletree-based BOS at I-TMT. This analysis assesses efficacy and performance differences between the two BOS configurations, involving a comprehensive examination of a 1520mm diameter polished glass roundel. The study integrates Finite Element Method (FEM) simulations with experimental data, providing insights into the efficiency of the respective BOS setups.

Next generation extreme precision radial velocity (EPRV) instruments such as the ANDES spectrograph of the Extremely Large Telescope will require an unprecedentedly high-precision calibration approach, particularly in the UB band region in which the most dense stellar absorption lines are present. For this purpose, astrocombs delivering thousands of atomically referenced, evenly-spaced calibration lines across a broad spectrum have the potential to be ideal calibration sources. Here, we report a novel and effective approach to generating a laser frequency comb with a multi- GHz mode spacing covering a broad wavelength range in the UB band. The approach is based on nonlinear mixing between near-infrared ultrafast laser pulses in a MgO:PPLN waveguide. The generated 1-GHz comb, spanning 390–520 nm, was filtered to a 30 GHz sub-comb using a low-dispersion Fabry-Perot etalon. The resultant UB-band astrocomb was then captured on a lab-built cross-dispersion echelle-prism spectrograph, demonstrating well resolved comb lines across the etalon bandwidth of 392–472 nm.

Spectro-polarimeters in solar astronomy usually require splitting different wavebands into separate monochromatic arms that operate as independent sub-instruments. We demonstrate a concept for a polarimeter that operates at two wavebands simultaneously, using a single channel of optical components and a single detector. By using chromatic zero-order waveplates, polarized light propagates differently through the instrument depending on its wavelength, allowing to measure the polarization in both wavebands simultaneously. We present Stokes vectors measurements with ∼ 1% relative error using standard off-the-shelf components, thus demonstrating the relevance of this concept for fields like solar astronomy and space instrumentation.

Additive manufacturing (AM; 3D printing), which builds a structure layer-by-layer, has clear benefits in the production of lightweight mirrors for astronomy, as it can create optimised lightweight structures and combine multiple components into one. AM aluminium mirrors have been reported that demonstrate a 44% reduction in mass from an equivalent solid and the consolidation of nine parts into one. However, there is a limit on the micro-roughness that can be achieved using AM aluminium at ∼5nm RMS (root mean square; Sq), therefore, to target applications at shorter wavelengths alternative AM materials are required. New capabilities in AM ceramics, silicon carbide infiltrated with silicon (SiC + Si) and fused silica, offer the possibility to combine the design benefits of AM with a material suitable for visible, ultraviolet and x-ray applications.
This paper will introduce the different printing methods and post-processing steps to convert AM ceramic samples into reflective mirrors. The samples are flat disks, 50mm diameter and 5mm in height, with three samples printed in SiC + Si and three printed in fused silica. Early results in polishing the SiC + Si material demonstrated that a micro-roughness of ∼2nm Sq could be achieved. To build on this study, the 50mm SiC + Si samples had three different AM finishing steps to explore the best approach for abrasive lapping and polishing, the reflective surfaces achieved demonstrated micro-roughness values varied between 2nm and 5nm Sq for the different AM finishing steps. To date, the printed fused silica material has heritage in lens applications; however, its suitability for mirror fabrication was to be determined. Abrasive lapping and polishing was used to process the fused silica to reflective surface and an average micro-roughness of <1nm Sq achieved on the samples.

WindCube is a NASA HFORT funded mission to study the coupling of thermospheric winds with the earth’s ionosphere. The optical system is based on a limb sensing Fabry-Perot etalon designed to measure the Doppler shift of the 630 nm oxygen airglow emission. The instrument payload is designed to fit within a 6U volume in a 12U CubeSat. The accuracy requirement for the wind speed retrieval is 5 m/s. This is the driving requirement for the opto-mechanical stability of the etalon system. Active temperature control of the etalon is employed to keep the mounted etalon within a +/- 0.1 C range. This paper discusses the design and analysis of the mounted etalon system to meet the accuracy requirement as well as surviving the rigors of vibration testing and the launch environment.

The standard design for 4-meter diameter class Imaging Atmospheric Cherenkov Telescopes (IACTs) used in groundbased gamma-ray astronomy is the dual-mirror Schwarzschild-Couder-like configuration. This design has been adopted for the telescopes in the ASTRI-Horn and ASTRI Mini-Array experiments (1 + 9 telescopes) and the construction of the 37 telescopes in the Small Size Telescope (SST) sub-array of the Cherenkov Telescope Array Observatory (CTAO) in Chile. The design provides an aplanatic optical response across a field of view wider than 10 degrees and is suitable for compact cameras using small pixels such as SiPM sensors. The telescopes feature secondary mirrors with a diameter of 1.8 meters, made of monolithic glass using a hot-slumping replication process. The paper discusses the manufacturing and characterization results of the prototype mirrors.

Developed largely for LSST follow-up, the SOAR Adaptive Module Optical Spectrograph (SAMOS) is a multiobject spectrograph that utilizes a Digital Micromirror Device (DMD) as a programmable slit mask for ground layer adaptive optics (GLAO) corrected observations. SAMOS covers a wavelength range spanning 400 – 950 nm, offering low-resolution (R ≈ 3,000) spectroscopy over the entire bandpass, and high-resolution (red: R ≈ 8,000, blue: R ≈ 9,000) spectroscopy over a limited wavelength range. The optical system is highly folded and very compact, forcing the use of a single spectroscopic camera to collect a full spectrum in two shots, using a grism exchange mechanism to switch between dispersion modes and resolving powers. To conserve space in this compact system the grisms (a pair of prisms bonded to a Volume Phase Holographic grating) are round, 70 mm in diameter, and mounted in the instrument by dead reckoning (i.e. no adjustment), to minimize optomechanical complexity. With no straight reference edges on either the prisms or the grating, this approach proved to be challenging from an alignment and bonding perspective. In this paper we present the method used to align and bond the SAMOS grisms. This method utilizes an elegant optical alignment technique to precisely align the VPH grating fringes to the prism facets during the bonding process, with minimal adhesive cleanup, zero bubbles in the clear aperture, and in the end producing exceptionally well-aligned spectra at the detector.

ARIEL is ESA’s fourth medium-class mission in the Cosmic Vision program, is scheduled for launch in 2029. The telescope aims to conduct an expansive, unbiased spectroscopic survey, unraveling the complexities of exoplanet atmospheres and interiors to better comprehend the key factors influencing planetary system formation and evolution. The baseline payload features an off-axis Cassegrain telescope (M1-M2), a collimating off-axis parabola (M3), and a plane folding mirror (M4) channeling the collimated beam into two instrument modules. ARIEL’s capabilities span primary and secondary transit spectroscopy (1.10 to 7.80μm), broad-band photometry in the Optical (0.50 − 0.80μm) and Near IR (0.80 − 1.10μm) ranges, and a Fine Guidance System. This work will focus on M1, an aluminum mirror with an unobscured elliptical shape of size 1100 x 730mm. The Surface Error budget for M1 covers low and mid spatial frequencies. The work describes the manufacturing process of the mirror, the method used to quantify surface roughness, the characterization of MSF errors, and the study of the degradation of the system performance due to MSF errors.

For aspherical and freeform surfaces not only the surface form error but also the position of the surface relative to external references is . These fiducials can be markers, the outside edge, plane orthogonal surfaces, dowel pin holes etc. The NMF non-contact measurement machine range for freeform optics by Dutch United Instruments (DUI) can be employed for measurements during the entire production process, measuring ground, polished and coated optical surfaces. DUI recently introduced the NMF1000 S, capable of measuring aspherical and freeform surfaces up to 1000 mm diameter. This platform has now been extended with a tactile probe option to measure reference features that are not measurable with the optical probe. This allows for nanometer level characterization of surface form, mid-spatial content and absolute position relative to the mechanical reference points. . Tactile probe results are discussed in this paper.

A Micro-lens Array (MLA) is an optical element in which multiple lens segments are integrated onto a single substrate. Traditional MLAs consist of segments with the same geometric shape arranged at regular intervals atop a planar surface. They are used for applications that include beam homogenization, to equalize light intensity distribution, and light field imaging to change post-exposure the optical configuration such as viewpoint and focal distance of the captured image data. However, the limitations imposed by the identical segment geometry and the regular arrangement pattern constrain the range of possible applications and their associated performance. In this paper, novel MLA geometries and design methods are introduced that enable new generation products. With this type of MLA, each segment can have a different free planar shape and freeform surface shape in height direction. The segments of MLA are designed with topology optimization method based on internal stresses, that allows unsupervised design of optical segments. The designed freeform segments can maximize the use of light the lens, according to the target illumination pattern and intensity defined by each segment.

Hexagonal cutting of pre-polished circular segments is one of the critical process step in the manufacturing of ELT-M1 mirrors. This enables edge-to-edge optical performance, and precise mechanical references used to align the segment during operation of the segmented primary mirror. This paper presents the novel technology developed by Safran REOSC to guarantee fast and precise referencing of all critical features, hexagonal shaping, edge sensor interface machining, cutouts handling, and throughput over one segment per day. We will analyse the machining performance over 100 mirrors, and the effect of cutting on optical surface.

Flat, Lightweight optics have the potential to significantly reduce the cost of space-based observing by allowing for reduced vehicle sizes and launch costs. We have designed, manufactured, and tested a metamaterial flat lens which operates at 480GHz. 480GHz was chosen as an intermediate step to designing a 557GHz lens, which is a frequency that has scientific importance as it is a ground-state water transition line, but nearly impossible to observe from the ground or from a balloon due to water in the atmosphere. The lens is constructed from polyimide (generic Kapton) and aluminum. The metamaterial design consists of ten layers of sub-wavelengthsized aluminum squares, sized via optimization to achieve the ideal phase transformation to create a 150mm focal distance at 480GHz. This optimization process also creates an effective anti-reflection quality. The lens has an aperture size of 124mm and an f-number of f/1.2. It weighs approximately three grams and is 110 microns thick. We have demonstrated the lens has near diffraction-limited beam performance with roughly 2.5dB of loss. The loss was measured using a radiometric y-factor method, using a room-temperature absorber as the hot load and an absorber submersed in liquid nitrogen as the cold load. The beam performance was measured using a near-field scan of the lens with a waveguide probe at the focus to illuminate the lens and a second probe to measure the phase and magnitude of the near-field collimated output. The loss was roughly 1.5 dB higher than expected in our design simulations.

Additive manufacture (AM) involves creating a part layer by layer and is a rapidly evolving manufacturing process. It has multiple strengths that apply to space-based optics, such as the ability to consolidate multiple parts into one, reducing the number of interfaces. The process also allows for greater mass reduction, making parts more cost-effective to launch, achieved by optimising the shape for intended use or creating intricate geometries like lattices. However, previous studies have highlighted issues associated with the AM process. For example, when trying to achieve high-precision optical surfaces on AM parts, the latticing on the underside of mirrors can provide insufficient support during machining, resulting in the quilting effect. This paper builds on previous work and explores such challenges further. This will be implemented by investigating ways to apply AM to a deployable mirror from a CubeSat project called A-DOT. The reflective surface has a spherical radius of curvature of 682 mm and approximate external dimensions of 106 x 83 mm. The aim is to produce two mirrors that will take full advantage of AM design benefits and account for the challenges in printing and machining a near-net shape. The designs will have reduced mass by using selected internal lattice designs and topologyoptimised connection points, resulting in two mirrors with mass reduction targets of 50% and 70%. Once printed in aluminium using laser powder bed fusion, the reflective surface will be created using single point diamond turning. Finally, an evaluation of the dimensional accuracy will be conducted, using interferometry, to quantify the performance of the reflective surface.

Additive manufacturing (AM; 3D printing) in aluminium using laser powder bed fusion provides a new design space for lightweight mirror production. Printing layer-by-layer enables the use of intricate lattices for mass reduction, as well as organic shapes generated by topology optimisation, resulting in mirrors optimised for function as opposed to subtractive machining. However, porosity, a common AM defect, is present in printed aluminium and it is a result of the printing environment being either too hot or too cold, or gas entrapped bubbles within the aluminium powder. When present in an AM mirror substrates, porosity manifests as pits on the reflective surface, which increases micro-roughness and therefore scattered light. There are different strategies to reduce the impact of porosity: elimination during printing, coating the aluminium print in nickel phosphorous, or to apply a heat and pressure treatment to close the pores, commonly known as a hot isostatic press (HIP).

This paper explores the application of HIP on printed aluminium substrates intended for mirror production using single point diamond turning (SPDT). The objective of the HIP is to reduce porosity whilst targeting a small grain growth within the aluminium, which is important in allowing the SPDT to generate surfaces with low micro-roughness. For this study, three disks, 50 mm diameter by 5 mm, were printed in AlSi10Mg at 0◦, 45◦, and 90◦ with respect to the build plate. X-ray computed tomography (XCT) was conducted before and after the HIP cycle to confirm the effectiveness of HIP to close porosity. The disks were SPDT and the micro-roughness evaluated. Mechanical testing and electron backscatter diffraction (EBSD) was used to quantify the mechanical strength and the grain size after HIP.

Ion Beam Figuring is a key technology after polishing, hexagonal cutting and integration to obtain ELT-M1 hexagonal segments without edge effects. This process used at REOSC over 30 years offers an efficient solution for finishing these large freeform optical components. This paper presents a dedicated figuring process strategy to maximize throughput and process convergence as well as to limit temperature increase during processing. We analysed the results of optical surface improvement over 100 ELT-M1 segments. These results highlight the high accuracy of IBF technology to correct hexagonal surfaces all the way to the edge. The final surface figure error below 10nm RMS was obtained while keeping low surface roughness. This is achieved after less than two figuring iterations leading to a throughput over one segment per day.