Low-wind effect is a strong limitation to direct imaging of exoplanets from ground-based telescopes, such as the Subaru telescope, the Very Large Telescope and probably the future extremely large telescopes. To mitigate it, we propose to design coronagraphs passively robust to low-wind effect. The Redundant Apodized Pupils (RAPs) are built so each pupil petal independently contributes to the contrast and therefore petal-level errors do not impact the final coronagraphic image, up to the loss of coherence in the star image. In this paper, we present the first experimental validation of the RAP concept, which is now applied on the Subaru/SCExAO instrument. We have designed three RAPs: two for the infrared channel (CHARIS) and one for the visible instrument (VAMPIRES). After these designs having been set up on the instrument in September 2023, we conducted internal source tests and obtained a contrast robustness up to a few radians. After this first experimental application, the RAP technology will be adapted, at higher contrasts (10−8-10−9), to segment-level errors, one of the main limitations for space segmented telescopes like the Habitable Worlds Observatory.
NASA is embarking on an ambitious program to develop the Habitable Worlds Observatory (HWO) flagship to perform transformational astrophysics, as well as directly image ∼ 25 potentially Earth-like planets and spectroscopically characterize them for signs of life. This mission was recommended by Astro2020, which additionally recommended a new approach for flagship formulation based on increasing the scope and depth of early, pre-phase A trades and technology maturation. A critical capability of the HWO mission is the suppression of starlight. To inform future architecture trades, it is necessary to survey a wide range of candidate technologies, from the relatively mature ones such as the ones described in the LUVOIR and HabEx reports to the relatively new and emerging ones, which may lead to breakthrough performance. In this paper, we present a summary of an effort, funded by NASA’s Exoplanet Exoplaration Program (ExEP), to survey potential coronagraph options for HWO. In particular, our results consist of: (1) a database of different coronagraph designs sourced from the world-wide coronagraph community that are potentially compatible with HWO; (2) evaluation criteria, such as expected mission yields and feasibility of maturing to TRL 5 before phase A; (3) a unified modeling pipeline that processes the designs from (1) and outputs values for any machine-calculable criteria from (2); (4) assessments of maturity of designs, and other criteria that are not machine-calculable; (5) a table presenting an executive summary of designs and our results. While not charged to down-select or prioritize the different coronagraph designs, the products of this survey were designed to facilitate future HWO trade studies.
We present upgrades to the visible-light (600nm to 800 nm) high-contrast imaging polarimeter, VAMPIRES, installed on the Subaru Coronagraphic Extreme Adaptive Optics instrument (SCExAO). These upgrades included low read noise, high dynamic range qCMOS detectors, a novel dichroic-based multiband imaging optic for spectral differential imaging, a suite of classic Lyot coronagraphs, and an achromatic fast polarization modulator. VAMPIRES is capable of diffraction-limited imaging (17 mas to 22 mas angular resolution) and achieves Strehl ratios up to ∼60% with 5σ coronagraphic contrast of 10-4 at 0.1′′ and 10-6 at >0.4′′. We highlight commissioning results from HD 169142, R Aqr, Neptune, and HD 1160B.
To reduce the amount of stellar light for exoplanet detection, coronagraphs feature amplitude masks in pupils plane(s) and/or focal plane(s), where a large fraction of photons are stopped -- and generally not used. Here, we give an overview of where potentially useful stellar (and circumstellar) photons are lost. We review existing concepts that use these lost photons, and propose generic strategies to make use of them for various applications. We particularly focus on wavefront sensing applications, but also explore how these photons can be used for calibration measurements, or for additional scientific observations.
Looking to the future of exo-Earth imaging from the ground, core technology developments are required in visible Extreme Adaptive Optics (ExAO) to enable the observation of atmospheric features such as oxygen on rocky planets in visible light. UNDERGROUND (Ultra-fast AO techNology Determination for Exoplanet imageRs from the GROUND), a collaboration built in Feb. 2023 at the Optimal Exoplanet Imagers Lorentz Workshop, aims to (1) motivate oxygen detection in Proxima Centauri b and analogs as an informative science case for high-contrast imaging and direct spectroscopy, (2) overview the state of the field with respect to visible exoplanet imagers, and (3) set the instrumental requirements to achieve this goal and identify what key technologies require further development.
The detection and characterization of Earth-like exoplanets around Sun-like stars is a primary science motivation for the Habitable Worlds Observatory. However, the current best technology is not yet advanced enough to reach the 10−10 contrasts at close angular separations and at the same time remain insensitive to low-order aberrations, as would be required to achieve high-contrast imaging of exo-Earths. Photonic technologies could fill this gap, potentially doubling exo-Earth yield. We review current work on photonic coronagraphs and investigate the potential of hybridized designs which combine both classical coronagraph designs and photonic technologies into a single optical system. We present two possible systems. First, a hybrid solution which splits the field of view spatially such that the photonics handle light within the inner working angle and a conventional coronagraph that suppresses starlight outside it. Second, a hybrid solution where the conventional coronagraph and photonics operate in series, complementing each other and thereby loosening requirements on each subsystem. As photonic technologies continue to advance, a hybrid or fully photonic coronagraph holds great potential for future exoplanet imaging from space.
Laboratory testbeds are an integral part of conducting research and developing technology for high-contrast imaging and extreme adaptive optics. There are a number of laboratory groups around the world that use and develop resources that are imminently required for their operations, such as software and hardware controls. The CAOTIC(Community of Adaptive OpTics and hIgh Contrast testbeds) project is aimed to be a platform for this community to connect, share information, and exchange resources in order to conduct more efficient research in astronomical instrumentation, while also encouraging best practices and strengthening cross-team connections. In these proceedings, we present the goals of the CAOTIC project, our new website, and we focus in particular on a new approach to teaching version control to scientists, which is a cornerstone of successful collaborations in astronomical instrumentation.
Oncoming exoplanet spectro-imagers like the Planetary Camera and Spectrograph (PCS) for the Extremely Large Telescope (ELT) will aim for a new class of exoplanets, including Earth-like planets evolving around M dwarfs i.e., closer than 0.1” with contrasts around 10−8. This goal can be achieved with coronagraphs to modulate the incident wavefront. However classical coronagraphs are not optimal: 1) they impose a planetary photon loss, which is particularly problematic when the instrument includes a high spectral-resolution spectrograph, 2) some aberrations such as the missing segments of the ELT are dynamic and not compatible with a static coronagraph design, 3) the coupling of the exoplanet image with a fiber for spectroscopy only requires the electric field to be controlled on a small target-dependent region of the detector. Such instruments would benefit from an adaptive tool to modulate the wavefront in both amplitude and phase. We propose to combine in the pupil plane a deformable mirror (DM) to control the phase and a digital micromirror device (DMD) i.e., an array made of 1920 × 1080 micro-mirrors able to switch between two positions, to control its amplitude. If the DM is already well-known in the field in particular for adaptive optics applications, the DMD has so far not been fully considered. At IPAG, we are currently assembling a testbed called CIDRE (Coronagraphy for DiRect Imaging of Exoplanets) to develop, test, calibrate, and validate the combination of these two components with a Lyot coronagraph. Since March 2022, CIDRE is assembled albeit without the Lyot coronagraph yet. The first few months have been dedicated to the calibration of the DMD. Since May 2022, it is operational and used to test dynamic amplitude apodization coronagraphs (so-called Shaped Pupils). This proceeding presents the set up of the CIDRE testbench and the first experimental results on adaptive Shaped Pupils obtained with the DMD.
The imaging and characterization of a larger range of exoplanets, down to young Jupiters and exo-Earths will require accessing very high contrasts at small angular separations with an increased robustness to aberrations, three constraints that drive current instrumentation development. This goal relies on efficient coronagraphs set up on extremely large diameter telescopes such as the Thirty Meter Telescope (TMT), the Giant Magellan Telescope (GMT), or the Extremely Large Telescope (ELT). However, they tend to be subject to specific aberrations that drastically deteriorate the coronagraph performance: their primary mirror segmentation implies phasing errors or even missing segments, and the size of the telescope imposes large spiders, generating low-wind effect as already observed on the Very Large Telescope (VLT)/SPHERE instrument or at the Subaru telescope, or adaptive-optics-due petaling, studied in simulations in the ELT case. The ongoing development of coronagraphs has then to take into account their sensitivity to such errors. We propose an innovative method to generate coronagraphs robust to primary mirror phasing errors and low-wind and adaptive-optics-due petaling effect. This method is based on the apodization of the segment or petal instead of the entire pupil, this apodization being then repeated to mimic the pupil redundancy. We validate this so-called Redundant Apodized Pupil (RAP) method on a James Webb Space Telescope-like pupil composed of 18 hexagonal segments segments to align, and on the VLT architecture in the case of residual low-wind effect.
We present recent laboratory results demonstrating high-contrast coronagraphy for the future space-based large IR/Optical/Ultraviolet telescope recommended by the Decadal Survey. The High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed aims to implement a system-level hardware demonstration for segmented aperture coronagraphs with wavefront control. The telescope hardware simulator employs a segmented deformable mirror with 37 hexagonal segments that can be controlled in piston, tip, and tilt. In addition, two continuous deformable mirrors are used for high-order wavefront sensing and control. The low-order sensing subsystem includes a dedicated tip-tilt stage, a coronagraphic target acquisition camera, and a Zernike wavefront sensor that is used to measure and correct low-order aberration drifts. We explore the performance of a segmented aperture coronagraph both in “static” operations (limited by natural drifts and instabilities) and in “dynamic” operations (in the presence of artificial wavefront drifts added to the deformable mirrors), and discuss the estimation and control strategies used to reach and maintain the dark-zone contrast using our low-order wavefront sensing and control. We summarize experimental results that quantify the performance of the testbed in terms of contrast, inner/outer working angle and bandpass, and analyze limiting factors.
Since 2019, GRAVITY has obtained unprecedented direct observations of exoplanets at high contrasts (down to 5 × 10−5) and small angular separations from the host star (down to 110 mas). To access deeper contrast (10−6) at smaller angular separations (less than 100 mas), we propose to dig a dark hole at the planet position. It relies on wavefront control using the adaptive optics deformable mirror to minimize the stellar flux injected in the GRAVITY interferometric combiner. We tested this technique on-sky on the instrument and concluded that the maximal contrast improvement it can achieve is ×4 on the current adaptive optics (NAOMI, MACAO). We also predict that the dark hole technique will bring a contrast improvement up to ×100 at less than 140 mas on the future GRAVITY+ adaptive optics of the Unit Telescopes.
We present recent laboratory results demonstrating high-contrast coronagraphy for future space-based large segmented telescopes such as the Large UV, Optical, IR telescope (LUVOIR) mission concept studied by NASA. The High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed aims to implement a system-level hardware demonstration for segmented aperture coronagraphs with wavefront control. The telescope hardware simulator employs a segmented deformable mirror with 36 hexagonal segments that can be controlled in piston, tip, and tilt. In addition, two continuous deformable mirrors are used for high-order wavefront sensing and control. The low-order sensing subsystem includes a dedicated tip-tilt stage, a coronagraphic target acquisition camera, and a Zernike wavefront sensor that is used to measure low-order aberration drifts. We explore the performance of a segmented aperture coronagraph both in “static” operations (limited by natural drifts and instabilities) and in “dynamic” operations (in the presence of artificial wavefront drifts added to the deformable mirrors), and discuss the estimation and control strategies used to reach and maintain the dark zone contrast. We summarize experimental results that quantify the performance of the testbed in terms of contrast, inner/outer working angle and bandpass, and analyze limiting factors by comparing against our end-to-end models.
This paper introduces an analytical method to calculate segment-level wavefront error (WFE) tolerances to enable the detection of faint extra-solar planets using segmented-aperture telescopes in space. This study provides a full treatment of the case of spatially uncorrelated segment phasing errors for segmented telescope coronagraphy, which has so far only been approached using ad-hoc Monte Carlo (MC) simulations. Instead of describing the wavefront tolerance globally for all segments, our method produces spatially dependent requirement maps. We relate the statistical mean contrast in the coronagraph dark hole to the standard deviation of the WFE of each individual segment on the primary mirror. This statistical framework for segment-level tolerancing extends the Pair-based Analytical model for Segmented Telescope Imaging from Space (PASTIS), which is based uniquely on a matrix multiplication for the optical propagation. We confirm our analytical results with MC simulations of end-to-end optical propagations through a coronagraph. Comparing our results for the Apodized Pupil Lyot Coronagraph designs for the Large Ultraviolet Optical Infrared telescope to previous studies, we show general agreement but we provide a relaxation of the requirements for a significant subset of segments in the pupil. These requirement maps are unique to any given telescope geometry and coronagraph design. The spatially uncorrelated segment tolerances we calculate are a key element of a complete error budget that will also need to include allocations for correlated segment contributions. We discuss how the PASTIS formalism can be extended to the spatially correlated case by deriving the statistical mean contrast and its variance for a non-diagonal aberration covariance matrix. The PASTIS tolerancing framework therefore brings a new capability that is necessary for the global tolerancing of future segmented space observatories.
This paper presents the setup for empirical validations of the Pair-based Analytical model for Segmented Telescope Imaging from Space (PASTIS) tolerancing model for segmented coronagraphy. We show the hardware configuration of the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed on which these experiments will be conducted at an intermediate contrast regime between 10-6 and 10-8. We describe the optical performance of the testbed with a classical Lyot coronagraph and describe the recent hardware upgrade to a segmented mode, using an IrisAO segmented deformable mirror. Implementing experiments on HiCAT is made easy through its top-level control infrastructure that uses the same code base to run on the real testbed, or to invoke the optical simulator. The experiments presented in this paper are run on the HiCAT testbed emulator, which makes them ready to be performed on actual hardware. We show results of three experiments with results from the emulator, with the goal to demonstrate PASTIS on hardware next. We measure the testbed PASTIS matrix, and validate the PASTIS analytical propagation model by comparing its contrast predictions to simulator results. We perform the tolerancing analysis on the optical eigenmodes (PASTIS modes) and on independent segments, then validate these results in respective experiments. This work prepares and enables the experimental validation of the analytical segment-based tolerancing model for segmented aperture coronagraphy with the specific application to the HiCAT testbed.
The search for Earth-like exoplanets requires high-contrast and high-angular resolution instruments, which designs can be very complex: they need an adaptive optics system to compensate for the effect of the atmospheric turbulence on image quality and a coronagraph to reduce the starlight and enable the companion imaging. During the instrument design phase and the error budget process, studies of performance as a function of optical errors are needed and require multiple end-to-end numerical simulations of wavefront errors through the optical system. In particular, the detailed analysis of long-exposure images enables to evaluate the image quality (photon noise level, impact of optical aberrations and of adaptive optics residuals, etc.). Nowadays simulating one long but finite exposure image means drawing several thousands of random frozen phase screens, simulating the image associated with each of them after propagation through the imaging instrument, and averaging all the images. Such a process is time consuming, demands a great deal of computer resources, and limits the number of parametric optimization. We propose an alternative and innovative method to directly express the statistics of ground-based images for long but finite exposure times. It is based on an analytical model, which only requires the statistical properties of the atmospheric turbulence. Such a method can be applied to optimize the design of future instruments such as SPHERE+ (VLT) or the planetary camera and spectrograph (PCS - ELT) or any ground-based instrument.
Direct imaging of exo-Earths and search for life is one of the most exciting and challenging objectives for future space observatories. Segmented apertures in space will be required to reach the needed large diameters beyond the capabilities of current or planned launch vehicles. These apertures present additional challenges for high-contrast coronagraphy, not only in terms of static phasing but also in terms of their stability. The Pair-based Analytical model for Segmented Telescope Imaging from Space (PASTIS) was developed to model the effects of segment-level optical aberrations on the final image contrast. In this paper, we extend the original PASTIS propagation model from a purely analytical to a semi-analytical method, in which we substitute the use of analytical images with numerically simulated images. The inversion of this model yields a set of orthonormal modes that can be used to determine segment-level wavefront tolerances. We present results in the case of segment-level piston error applied to the baseline coronagraph design of LUVOIR A, with minimum and maximum wavefront error constraint between 56 pm and 290 pm per segment. The analysis is readily generalizable to other segment-level aberrations modes, and can also be expanded to establish stability tolerances for these missions.
The goal of the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed is to demonstrate coronagraphic starlight suppression solutions for future segmented aperture space telescopes such as the Large UV, Optical, IR telescope (LUVOIR) mission concept being studied by NASA. The testbed design has the flexibility to enable studies with increasing complexity for telescope aperture geometries starting with off-axis telescopes, then on-axis telescopes with central obstruction and support structures. The testbed implements the Apodized Pupil Lyot Coronagraph (APLC) optimized for the HiCAT aperture, which is similar to one of the possible geometries considered for LUVOIR. Wavefront can be controlled using continuous deformable mirrors, and wavefront sensing is performed using the imaging camera, or a dedicated phase retrieval camera, and also in a low-order wavefront sensing arm. We present a progress update of the testbed in particular results using two deformable mirror control to produce high-contrast dark zone, and preliminary results using the testbed’s low order Zernike wavefront sensor.
Segmented telescopes are a possible approach to enable large-aperture space telescopes for the direct imaging and spectroscopy of habitable worlds. However, the increased complexity of their aperture geometry, due to the central obstruction, support structures and segment gaps, makes high-contrast imaging very challenging. The High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed was designed to study and develop solutions for such telescope pupils using wavefront control and coronagraphic starlight suppression. The testbed design has the flexibility to enable studies with increasing complexity for telescope aperture geometries starting with off-axis telescopes, then on-axis telescopes with central obstruction and support structures - e.g. the Wide Field Infrared Survey Telescope (WFIRST) - up to on-axis segmented telescopes, including various concepts for a Large UV, Optical, IR telescope (LUVOIR). In the past year, HiCAT has made significant hardware and software updates in order to accelerate the development of the project. In addition to completely overhauling the software that runs the testbed, we have completed several hardware upgrades, including the second and third deformable mirror, and the first custom Apodized Pupil Lyot Coronagraph (APLC) optimized for the HiCAT aperture, which is similar to one of the possible geometries considered for LUVOIR. The testbed also includes several external metrology features for rapid replacement of parts, and in particular the ability to test multiple apodizers readily, an active tip-tilt control system to compensate for local vibration and air turbulence in the enclosure. On the software and operations side, the software infrastructure enables 24/7 automated experiments that include routine calibration tasks and high-contrast experiments. In this communication we present an overview and status update of the project, both on the hardware and software side, and describe the results obtained with APLC wavefront control.
KEYWORDS: Wavefronts, James Webb Space Telescope, Monochromatic aberrations, Point spread functions, Wavefront sensors, Mirrors, Cameras, Space telescopes, Telescopes, Phase retrieval
The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a hardware simulator for wavefront sensing and control designed to produce JWST-like images. A model of the JWST three mirror anastigmat is realized with three lenses in the form of a Cooke triplet, which provides JWST-like optical quality over a field equivalent to a NIRCam module. An Iris AO hexagonally segmented mirror stands in for the JWST primary. This setup successfully produces images extremely similar to expected JWST in- ight point spread functions (PSFs), and NIRCam images from cryotesting, in terms of the PSF morphology and sampling relative to the diffraction limit. The segmentation of the primary mirror into subapertures introduces complexity into wavefront sensing and control (WFSandC) of large space based telescopes like JWST. JOST provides a platform for independent analysis of WFSandC scenarios for both commissioning and maintenance activities on such observatories. We present an update of the current status of the testbed including both single field and wide-field alignment results. We assess the optical quality of JOST over a wide field of view to inform the future implementation of different wavefront sensing algorithms including the currently implemented Linearized Algorithm for Phase Diversity (LAPD). JOST complements other work at the Makidon Laboratory at the Space Telescope Science Institute, including the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed, that investigates coronagraphy for segmented aperture telescopes. Beyond JWST we intend to use JOST for WFSandC studies for future large segmented space telescopes such as LUVOIR.
KEYWORDS: Image segmentation, Coronagraphy, Telescopes, Space telescopes, Systems modeling, Error analysis, Monochromatic aberrations, Zernike polynomials, James Webb Space Telescope, Mirrors
The imaging and spectroscopy of habitable worlds will require large-aperture space-based telescopes, to increase the collecting area and the angular resolution. These large telescopes will necessarily use segmented primaries to fit in a rocket. However, these massively segmented mirrors make high-contrast performance very difficult to achieve and stabilize, compared with more common monolithic primaries. Despite space telescopes operating in a friendlier environment than ground-based telescopes, remaining vibrations and resonant modes on the segments can still deteriorate the performance. In this context, we present the Pair-based Analytical model for Segmented Telescopes Imaging from Space (PASTIS) that enables the establishment of a comprehensive error budget, both in terms of segment alignment and stability. Using this model, one may evaluate the influence of the segment cophasing and surface quality evolution on the final images and contrasts, and set up requirements for any given mission. One can also identify the dominant modes of a given geometry for a given coronagraphic instrument and design the feedback control systems accordingly. We first develop and validate this analytical model by comparing its outputs to the images and contrasts predicted by an end-to-end simulation. We show that the contrasts predicted using PASTIS are accurate enough compared with the end-to-end propagation results, at the exo-Earth detection level. Second, we develop a method for a fast and efficient error budget in terms of segment manufacturing and alignment that takes into account the disparities of the segment effects on the final performance. This technique is then applied on a specific aperture to provide static and quasistatic requirements on each segment for local piston and 45-deg astigmatism aberrations. Finally, we discuss potential application of this technique to future missions.
We discuss the use of parametric phase-diverse phase retrieval as an in-situ high-fidelity wavefront measurement method to characterize and optimize the transmitted wavefront of a high-contrast coronagraphic instrument. We apply our method to correct the transmitted wavefront of the HiCAT (High contrast imager for Complex Aperture Telescopes) coronagraphic testbed. This correction requires a series of calibration steps, which we describe. The correction improves the system wavefront from 16 nm RMS to 3.0 nm RMS.
New space missions dedicated to exoplanet imaging will rely on coronagraphs to address the high contrast between the stars and their environments. In order to avoid the image of planets to be lost in post-coronagraphic starlight residuals, high precision wavefront sensing and control is a key element to these missions. We present recent results of simultaneous post-coronagraphic phase and amplitude sensing obtained on the THD bench using the coronagraphic phase diversity. We also present results of simulation studies on the non-linear dark hole technique to assess the main limitations of this technique. Finally, we present a first experimental validation of its principle and corroborate expectations on its speed of convergence. These results suggest that the non-linear dark hole is a good candidate for wave-front control for future space-based exoplanet imaging missions, where fast techniques to produce deep dark holes are of paramount importance.
Direct imaging and spectroscopy of Earth-like planets will require high-contrast imaging at very close angular separation: 1e10 star to planet ux ratio at a few tenths of an arcsecond. Large telescopes in space are necessary to provide sufficient collecting area and angular resolution to achieve this goal. In the static case, coronagraphic instrument designs combined with wavefront control techniques have been optimized for segmented on-axis telescope geometries, but the extreme wavefront stability required at very high contrast of the order of tens of picometers remains one of the main challenges. Indeed, cophasing errors and instabilities directly contribute to the degradation of the final image contrast. A systematic understanding is therefore needed to quantify and optimize the static and dynamic constraints on segment phasing. We present an analytical model: Pair-based Analytical model for Segmented Telescopes Imaging from Space (PASTIS), which enables quasi-instantaneous analytical evaluations of the impact of segment-level aberrations and phasing on the image contrast. This model is based on a multiple sum of Young interference fringes between pairs of segments and produces short and long exposure coronagraphic images with a segmented telescope in presence of local phase aberrations on each segment. PASTIS matches end-to-end numerical simulations with high-fidelity (3% rms error on the contrast). Moreover, the model can be inverted by dint of a projection on the singular modes of the phase to provide constraints on each Zernike polynomial for each segment. These singular modes provide information on the contrast sensitivity to segment-level phasing errors in the pupil, which can be used to derive constraints on both static and dynamic mitigation strategies (e.g. backplane geometry or segment vibration sensing and control). The few most sensitive modes can be well identified and must be controlled at the level of tens of picometers, while the least sensitive modes in the hundreds of picometers. This novel formalism enables a fast and efficient sensitivity analysis for any segmented telescopes, in both static and dynamic modes.
The current generation of terrestrial telescopes has large enough primary mirror diameters that active optical control based on wavefront sensing is necessary. Similarly, in space, while the Hubble Space Telescope (HST) has a mostly passive optical design, apart from focus control, its successor the James Webb Space Telescope (JWST) has active control of many degrees of freedom in its primary and secondary mirrors.
The next generation of space telescopes for direct imaging and spectroscopy of exoplanets includes telescopes with a monolithic mirror, such as the Wide Field Infrared Survey Telescope (WFIRST) [1] and Large Ultra-Violet Optical Infrared (LUVOIR) telescopes with segmented primary mirror, like ATLAST [2, 3] or HDST [4].
The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop experiment designed to study wavefront sensing and control for a segmented space telescope, such as JWST. With the JWST Science and Operations Center co-located at STScI, JOST was developed to provide both a platform for staff training and to test alternate wavefront sensing and control strategies for independent validation or future improvements beyond the baseline operations. The design of JOST reproduces the physics of JWST’s three-mirror anastigmat (TMA) using three custom aspheric lenses. It provides similar quality image as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at 633 nm. An Iris AO segmented mirror stands for the segmented primary mirror of JWST. Actuators allow us to control (1) the 18 segments of the segmented mirror in piston, tip, tilt and (2) the second lens, which stands for the secondary mirror, in tip, tilt and x, y, z positions. We present the most recent experimental results for the segmented mirror alignment. Our implementation of the Wavefront Sensing (WFS) algorithms using phase diversity is tested on simulation and experimentally. The wavefront control (WFC) algorithms, which rely on a linear model for optical aberrations induced by misalignment of the secondary lens and the segmented mirror, are tested and validated both on simulations and experimentally. In this proceeding, we present the performance of the full active optic control loop in presence of perturbations on the segmented mirror, and we detail the quality of the alignment correction.
Segmented telescopes enable large-aperture space telescopes for the direct imaging and spectroscopy of habitable worlds. However, the increased complexity of their aperture geometry, due to their central obstruction, support structures, and segment gaps, makes high-contrast imaging very challenging. In this context, we present an analytical model that will enable to establish a comprehensive error budget to evaluate the constraints on the segments and the influence of the error terms on the final image and contrast. Indeed, the target contrast of 1010 to image Earth-like planets requires drastic conditions, both in term of segment alignment and telescope stability. Despite space telescopes evolving in a more friendly environment than ground-based telescopes, remaining vibrations and resonant modes on the segments can still deteriorate the contrast. In this communication, we develop and validate the analytical model, and compare its outputs to images issued from end-to-end simulations.
The increasing complexity of the aperture geometry of the future space- and ground based-telescopes will limit the performance of the next generation of coronagraphic instruments for high contrast imaging of exoplanets. We propose here a new closed-loop optimization technique using two deformable mirrors to correct for the effects of complex apertures on coronagraph performance, alternative to the ACAD technique previously developed by our group. This technique, ACAD-OSM, allows the use of any coronagraphs designed for continuous apertures, with complex, segmented, apertures, maintaining high performance in contrast and throughput. We show the capabilities of this technique on several pupil geometries (segmented LUVOIR type aperture, WFIRST, ELTs) for which we obtained high contrast levels with several deformable mirror setups (size, number of actuators, separation between them), coronagraphs (apodized pupil Lyot and vortex coronagraphs) and spectral bandwidths, which will help us present recommendations for future coronagraphic instruments. We show that this active technique handles, without any revision to the algorithm, changing or unknown optical aberrations or discontinuities in the pupil, including optical design misalignments, missing segments and phase errors.
AO systems aim at detecting and correcting for optical distortions induced by atmospheric turbulences. They are also extremely sensitive to extraneous sources of perturbation such as vibrations, which degrade the performance. The Gemini South telescope has currently two main AO systems: the Gemini Multi Conjugated AO System GeMS and the Gemini Planet Imager GPI. GeMS is operational and regularly used for science observation delivering close to diffraction limit resolution over a large field of view (85×85 arcsec2). Performance limitation due to the use of an integrator for tip-tilt control is here explored. In particular, this type of controller does not allow for the mitigation of vibrations with an arbitrary natural frequency. We have thus implemented a tip-tilt Linear Quadratic Gaussian (LQG) controller with different underlying perturbation models: (i) a sum of autoregressive models of order 2 identified from an estimated power spectrum density (s-AR2) of the perturbation,1 already tested on CANARY2 and routinely used on SPHERE;3 (ii) cascaded ARMA models of order 2 identified using prediction error minimization (c-PEM) as proposed in.4, 5 Both s-AR2 and c-PEM were parameterized to produce tip or tilt state-space models up to order 20 and 30 respectively. We discuss the parallelized implementation in the real time computer and the expected performance. On-sky tests are scheduled during the November 2016 run or the January 2017 run.
Segmented telescopes are a possible approach to enable large-aperture space telescopes for the direct imaging and spectroscopy of habitable worlds. However, the increased complexity of their aperture geometry, due to their central obstruction, support structures and segment gaps, makes high-contrast imaging very challenging.
The High-contrast imager for Complex Aperture Telescopes (HiCAT) was designed to study and develop solutions for such telescope pupils using wavefront control and starlight suppression. The testbed design has the flexibility to enable studies with increasing complexity for telescope aperture geometries starting with off-axis telescopes, then on-axis telescopes with central obstruction and support structures (e.g. the Wide Field Infrared Survey Telescope [WFIRST]), up to on-axis segmented telescopes e.g. including various concepts for a Large UV, Optical, IR telescope (LUVOIR), such as the High Definition Space Telescope (HDST). We completed optical alignment in the summer of 2014 and a first deformable mirror was successfully integrated in the testbed, with a total wavefront error of 13nm RMS over a 18mm diameter circular pupil in open loop. HiCAT will also be provided with a segmented mirror conjugated with a shaped pupil representing the HDST configuration, to directly study wavefront control in the presence of segment gaps, central obstruction and spider.
We recently applied a focal plane wavefront control method combined with a classical Lyot coronagraph on HiCAT, and we found limitations on contrast performance due to vibration effect. In this communication, we analyze this instability and study its impact on the performance of wavefront control algorithms. We present our Speckle Nulling code to control and correct for wavefront errors both in simulation mode and on testbed mode. This routine is first tested in simulation mode without instability to validate our code. We then add simulated vibrations to study the degradation of contrast performance in the presence of these effects.
The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop experiment designed to study wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science and Operations Center. The design of JOST reproduces the physics of JWST’s three-mirror anastigmat (TMA) using three custom aspheric lenses. It provides similar quality image as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at 633 nm. An Iris AO segmented mirror stands for the segmented primary mirror of JWST. Actuators allow us to control (1) the 18 segments of the segmented mirror in piston, tip, tilt and (2) the second lens, which stands for the secondary mirror, in tip, tilt and x, y, z positions. We present the full linear control alignment infrastructure developed for JOST, with an emphasis on multi-field wavefront sensing and control. Our implementation of the Wavefront Sensing (WFS) algorithms using phase diversity is experimentally tested. The wavefront control (WFC) algorithms, which rely on a linear model for optical aberrations induced by small misalignments of the three lenses, are tested and validated on simulations.
HiCAT is a high-contrast imaging testbed designed to provide complete solutions in wavefront sensing, control and starlight suppression with complex aperture telescopes. The pupil geometry of such observatories includes primary mirror segmentation, central obstruction, and spider vanes, which make the direct imaging of habitable worlds very challenging. The testbed alignment was completed in the summer of 2014, exceeding specifications with a total wavefront error of 12nm rms over a 18mm pupil. The installation of two deformable mirrors for wavefront control is to be completed in the winter of 2015. In this communication, we report on the first testbed results using a classical Lyot coronagraph. We also present the coronagraph design for HiCAT geometry, based on our recent development of Apodized Pupil Lyot Coronagraph (APLC) with shaped-pupil type optimizations. These new APLC-type solutions using two-dimensional shaped-pupil apodizer render the system quasi-insensitive to jitter and low-order aberrations, while improving the performance in terms of inner working angle, bandpass and contrast over a classical APLC.
Fast and easy preview of a fabric without having to produce samples would be very profitable for textile designers, but
remains a technological challenge. As a first step towards this objective, we study the possibility of making images of a
real sample, and changing virtually the colors of its yarns while preserving the shine and shadow texture. We consider
two types of fabrics: Jacquard weave fabrics made of polyester warp and weft yarns of different colors, and satin ribbons
made of polyester and metallic yarns. For the Jacquard fabric, we make a color picture with a scanner on a sample in
which the yarns have contrasted colors, threshold this image in order to distinguish the pixels corresponding to each
yarn, and accordingly modify their hue and chroma values. This method is simple to operate but do not enable to
simulate the angle-dependent shine. A second method, tested on the satin ribbon made of black polyester and achromatic
metallic yarns, is based on polarized imaging. We analyze the polarization state of the reflected light which is different
for dielectric and metallic materials illuminated by polarized light. We then add a fixed color value to the pixels
representing the polyester yarns and modify the hue and chroma of the pixels representing the metallic yarns. This was
performed for many incident angles of light, in order to render the twinkling effect displayed by these ribbons. We could
verify through a few samples that the simulated previews reproduce real pictures with visually acceptable accuracy.
We present a new high-contrast imaging testbed designed to provide complete solutions in wavefront sensing, control and starlight suppression with complex aperture telescopes. The testbed was designed to enable a wide range of studies of the effects of such telescope geometries, with primary mirror segmentation, central obstruction, and spiders. The associated diffraction features in the point spread function make high-contrast imaging more challenging. In particular the testbed will be compatible with both AFTA-like and ATLAST-like aperture shapes, respectively on-axis monolithic, and on-axis segmented telescopes. The testbed optical design was developed using a novel approach to define the layout and surface error requirements to minimize amplitude induced errors at the target contrast level performance. In this communication we compare the as-built surface errors for each optic to their specifications based on end-to-end Fresnel modelling of the testbed. We also report on the testbed optical and optomechanical alignment performance, coronagraph design and manufacturing, and preliminary first light results.
The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop workbench to study aspects of wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing optomechanical testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope, TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science & Operations Center. We have developed an optical design that reproduces the physics of JWST's three-mirror anastigmat using three aspheric lenses; it provides similar image quality as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at HeNe wavelength. A segmented deformable mirror stands in for the segmented primary mirror and allows control of the 18 segments in piston, tip, and tilt, while the secondary can be controlled in tip, tilt and x, y, z position. This will be sufficient to model many commissioning activities, to investigate field dependence and multiple field point sensing & control, to evaluate alternate sensing algorithms, and develop contingency plans. Testbed data will also be usable for cross-checking of the WFS&C Software Subsystem, and for staff training and development during JWST's five- to ten-year mission.
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