We are developing fabrication methods of a volume binary (VB) grating, trapezoid grating and reflector facet transmission (RFT) grating. The VB grating can achieve a larger angular dispersion and higher diffraction efficiency than conventional surface-relief transmission gratings with step shaped grooves, it can be achieved a wider spectral bandwidth than a volume phase holographic (VPH) grating whose refractive index is sinusoidally modulated. The trapezoid grating can bring the spectral characteristics of s- and p-polarization closer to each other than a VB grating, so it can further improve the peak diffraction efficiency.
The instrumentation of the Prime Focus Spectrograph (PFS), a next generation facility instrument on the Subaru telescope, is now in the final phase of its commissioning process and its general, open-use operations for sciences will provisionally start in 2025. The instrument enables simultaneous spectroscopy with 2386 individual fibers distributed over a very wide (∼1.3 degrees in diameter) field of view on the Subaru’s prime focus. The spectra cover a wide range of wavelengths from 380nm to 1260nm in one exposure in the Low-Resolution (LR) mode (while the visible red channel has the Medium-Resolution (MR) mode as well that covers 710−885nm). The system integration activities at the observatory on Maunakea in Hawaii have been continuing since the arrival of the Metrology Camera System in 2018. On-sky engineering tests and observations have also been carried out continually since September 2021 and, despite various difficulties in interlacing commissioning processes with development activities on the schedule and addressing some major issues on hardware and software, the team successfully observed many targeted stars as intended over the entire field of view (Engineering First Light) in September 2022. Then in parallel to the arrival, integration and commissioning of more hardware components, validations and optimizations of the performance and operation of the instrument are ongoing. The accuracy of the fiber positioning process and the speed of the fiber reconfiguration process have been recently confirmed to be ∼ 20−30μm for 95% of allocated fibers, and ∼130 seconds, respectively. While precise quantitative analyses are still in progress, the measured throughput has been confirmed to be consistent with the model where the information from various sub-components and sub-assemblies is integrated. Long integration of relatively faint objects are being taken to validate an expected increase of signal-to-noise ratio as more exposures are taken and co-added without any serious systematic errors from, e.g., sky subtraction process. The PFS science operation will be carried out in a queue mode by default and various developments, implementations and validations have been underway accordingly in parallel to the instrument commissioning activities. Meetings and sessions are arranged continually with the communities of potential PFS users on multiple scales, and discussions are iterated for mutual understanding and possible optimization of the rules and procedures over a wide range of processes such as proposal submission, observation planning, data acquisition and data delivery. The end-to-end processes of queue observations including successive exposures with updated plans based on assessed qualities of the data from past observations are being tested during engineering observations, and further optimizations are being undertaken. In this contribution, a top-level summary of these achievements and ongoing progresses and future perspectives will be provided.
ULTIMATE-Subaru is the next-generation facility instrument program of the Subaru Telescope which will extend the existing Subaru’s wide-field survey capability to the near-infrared wavelength. The ULTIMATE-Subaru instrument suite includes Ground-Layer Adaptive Optics (GLAO) and wide-field near-infrared instruments, aiming to provide ∼0.2 arcsec image size at K band (2.2 μm) over 20 arcmin diameter field of view at the Cassegrain focus. The planned first light instrument is a Wide-Field Imager (WFI), which covers a 14 × 14 square arcmin field of view from 0.9 to 2.5 μm in wavelength. GLAO and WFI are currently in the final design phase, aiming to start the commissioning observations at the telescope in 2028. In parallel to the development for ULTIMATE wide-field instruments, there are ongoing activities to develop a narrow-field wide-band spectrograph (NINJA) together with a Laser Tomography AO system (ULTIMATE-START) utilizing the Adaptive Secondary Mirror and the Laser Guide Star Facility being developed for the GLAO system. In this presentation, an overview of the ULTIMATE-SUBARU instruments, their current status, and future prospects will be presented.
ULTIMATE-Subaru is a next-generation wide-field NIR imaging camera with ground layer adaptive optics, being developed for the Subaru telescope. Here we present the current sensitivity performance estimates for the instrument. In the ideal conditions of good (25%) seeing with GLAO, airmass of 1 and an hour exposure time, we reach 5σ point source depths of 25.6, 25.5, 25.2 and 25.4 mags in YJHKs respectively. The ULTIMATE sensitivities show an improvement of 0.4−0.6 mag over MOIRCS in broad-band filters under the same observing conditions (without GLAO). With GLAO there is a further improvement of 0.2∼0.4 mags in depth across all bands compared to natural seeing, in addition to the significant enhancement in image quality, i.e. FWHM up to a factor of 2 over natural seeing. We have also modeled the fractional noise contribution in the NIR from sky background, telescope thermal background, moon background and read noise. We find that sky background is the dominant source of noise across most NIR bands, apart from the K-band, where the thermal emission from the telescope becomes a significant source of noise. Our results indicate that K-band observations using ULTIMATE-Subaru with GLAO under ideal observing conditions could potentially reach sensitivities comparable to those of the Roman telescope, given that instrument thermal emission remains an important noise component in both ground and space telescopes at this wavelength.
We have undertaken the development of high-efficiency and wide spectral coverage grisms for MOIRCS, the near-infrared imager and multi-object spectrograph at the Subaru Telescope. Our prior medium-resolution gratings, incorporating Volume Phase Holographic (VPH) gratings, offered very high efficiency at their peak. However, their narrow transmission curves significantly limited their scientific application, especially in the MOS mode. In response to the demand for better medium-dispersion grisms from the community, we developed new high-sensitivity and wide-spectral-coverage grisms (“LightSmyth grisms”) for the J & H windows in 2019. It was a great success, with significant improvement on both peak efficiency and the wide bandwidth coverage. Following this achievement, we embarked on the development of a comparable medium-dispersion grism for the K-band (“VB-K grism”), incorporating our proprietary Volume-Binary (VB) grating. The fabrication was completed by the summer of 2023. The basic performance test inside the dome confirmed its excellent performance as planned. The first scientific use by open-use observers was achieved in March 2024. A more detailed on-sky performance evaluation is scheduled this summer.
ULTIMATE-Subaru is a next facility instrumentation program of the Subaru Telescope. The goal of this project is to extend the wide-field capability of the Subaru to near-infrared (NIR), by developing a wide-field ground-layer adaptive optics (GLAO) system and wide-field NIR instruments. The GLAO system will uniformly improve the image quality up to 20-arcmin field of view in diameter by correcting for the ground-layer turbulence. The expected image quality after the GLAO correction is FWHM~0".2 in K-band under moderate seeing conditions. In this presentation, we present preliminary design overview of the GLAO system at the Cassegrain focus, which consist of an Adaptive Secondary Mirror, NGS and LGS wavefront sensor system, a laser guide star facility, and control system. We also present the prototyping activities to validate the selected design of the GLAO system.
Currently we are developing a VB grating for an echelle grism of the Subaru Multi-Object InfraRed Camera and Spectograph (MOIRCS) and a VB grating for the Advanced Lunar Imaging Spectrometer (ALIS) of the Lunar Polar Exploration Mission (LUPEX). The shapes of gratings are optimized to achieve high diffraction efficiency and a wide spectral bandwidth by performing numerical calculations of the rigorous coupled wave analysis (RCWA). Based on the calculated results, we are developing variety of gratings using MEMS technologies. In addition, we have deployed new high-dispersion grisms of J and H band of MOIRCS with transmission gratings fabricated by LightSmyth. The transmission grating is kind of a VB grating which ridges are composed by three kinds of dielectric layers.
Publisher’s Note: This paper, originally published on 13 December 2020, was replaced with a corrected/revised version on 18 May 2021. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
The Simultaneous-color Wide-field Infrared Multi-object Spectrograph (SWIMS) is one of the 1st generation facility instruments for the University of Tokyo Atacama Observatory (TAO) 6.5 m telescope currently being constructed at the summit of Cerro Chajnantor (5,640 m altitude) in northern Chile. SWIMS has two optical arms, the blue arm covering 0.9–1.4 µm and the red 1.4–2.5 µm, by inserting a dichroic mirror into the collimated beam, and thus is capable of taking images in two filter-bands simultaneously in imaging mode, or whole nearinfrared (0.9–2.5 µm) low-to-medium resolution multi-object spectra in spectroscopy (MOS) mode, both with a single exposure. SWIMS was carried into Subaru Telescope in 2017 for performance evaluation prior to completion of the construction of the 6.5 m telescope, and successfully saw the imaging first light in May 2018 and MOS first light in Jan 2019. After three engineering runs including the first light observations, SWIMS has been accepted as a new PI instrument for Subaru Telescope from the semester S21A until S22B. In this paper, we report on details of on-sky performance of the instrument evaluated during the engineering observations for a total of 7.5 nights.
Results of a conceptual design study of ULTAIMTE-Wide Field Imager (WFI) is presented. ULTIMATE-WFI is a near-infrared wide-field imager for the ground-layer adaptive optics system of the Subaru telescope (ULTIMATESubaru) which realizes a 0. 002 seeing size over 200diameter at the Cassegrain focus utilizing a deformable 2ndry mirror. WFI has a 15. 07×15. 07 FoV with a wavelength coverage of 0.9–2.5µm. The FoV is covered by four identical optics, each having a square field lens with 226mm on a side. Its effective FoV is 7. 02 on a side, and is covered by a HAWAII-4RG array detector with a pixel scale of 0. 0011/pix. Effective FoV will be 14. 04×14. 04 or 2070 in total. Spot sizes at a detector plane are less than 0. 001 over the wavelength coverage. Due to the large FoV, vignetting by the telescope structure occurs and an additional cold stop is necessary to block their thermal emission, which causes ~80% vignetting at the edge of the FoV. All the optics are contained in a cylindrical structure to be installed on the Cassegrain focus of the telescope, and kept under cryogenic temperature except for the field lenses. Gravitational deformation will be smaller than 1mm, and may have negligible impact on the final image quality.
The fabrication of the new medium-resolution grisms for MOIRCS onboard Subaru 8.2-m Telescope is presented. Our new grisms feature the state-of-the-art gratings that have very high efficiency and wide-spectral coverage manufactured by LightSmyth for the pulse-compression technology. The grating has the peak efficiency of over 96% and can cover the whole H-band wavelength range with over 90%. This is the first-time astronomical application case for the LightSmyth grating. We manufactured the custom-made H-band grism as well as the catalog product J-band grism with a bit less ideal performance. The cooling test of the grisms was done successfully, confirming the stability of the wave-front error over the cooling cycle. On-sky performance test of the new grisms were achieved in July 2020, and we have confirmed the high sensitivity as well as the amazing flatness of the throughput of these grisms. Though we cofirmed the existence of some faint ghosts of the 0-th order light as anticipated, the effect of them are confirmed to be negligible. We started offering the use of the grisms for Subaru community from August 2020.
ULTIMATE-Subaru is a next large facility instrument project at Subaru telescope. We will develop a 14x14 sq. arcmin wide-field near-infrared (NIR) imager and a multi-object spectrograph with the aid of a ground- layer adaptive optics system (GLAO), which will uniformly improve the seeing by a factor of 2 over a wide field of view up to ~20 arcmin in diameter. We have developed system modeling of the GLAO and wide-field NIR instruments to define the system level requirements flow down from science cases and derive the system performance budgets based on the GLAO end-to-end numerical simulation and optical system models of the telescope and wide-field NIR science instruments. In this paper, we describe the system performance modeling of ULTIMATE-Subaru and present an overview of the requirements flow down.
ULTIMATE-Subaru is a next large facility instrument project at Subaru telescope. We will develop a 14x14 arcmin2 wide-field near-infrared (1.0-2.5μm) imager and a multi-object spectrograph with the aid of a ground- layer adaptive optics system (GLAO), which will uniformly improve the seeing by a factor of 2 over a wide field of view up to ~20 arcmin in diameter. The expected spatial resolution by the GLAO correction is about 0.2 arcsec FWHM in K-band under moderate seeing conditions at Subaru telescope. ULTIMATE-Subaru will provide a unique capability to realize wide-field and high spatial resolution survey observations in near infrared in the era of TMT. In this paper, we introduce the project overview including the GLAO and near-infrared instrument conceptual design. We also describe the future wide-field strategy at Subaru telescope with ULTIMATE-Subaru together with HSC and PFS.
We report on the conceptual design study done for the Ground Layer Adaptive Optics system of the ULTIMATE-Subaru project. This is an ambitious instrument project, providing GLAO correction in a square field of view of 14 arcmin on a side, aiming to deliver improved seeing at the near infrared wavelength. Its client instruments are an imager and multi-IFU spectrograph at Cassegrain and a Multi-Object spectrograph at Nasmyth. In this paper, we introduce the ULTIMATE-Subaru project overview and its science case and report the results of the GLAO performance prediction based on the numerical simulation and conceptual design of the wavefront sensor system.
The Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is a first-generation near-infrared instrument for the University of Tokyo Atacama Observatory (TAO) 6.5m Telescope now being constructed in northern Chile. To utilize the advantage of the site that almost continuous atmospheric window appears from
0.9 to 2.5 μm, the instrument is capable of simultaneous two-color imaging with a field-of-view of 9.′6 in diameter or λ/▵λ 1000 multi-object spectroscopy at 0.9–2.5 μm in a single exposure. The instrument has been trans- ported in 2017 to the Subaru Telescope as a PI-type instrument for carrying out commissioning observations before starting science operation on the 6.5m telescope. In this paper, we report the latest updates on the instrument and present preliminary results from the on-sky performance verification observations.
We will introduce current status of development of a birefringence volume phase holographic (B-VPH) grating, volume binary (VB) grating and reflector facet transmission (RFT) grating developing as the novel dispersive optical element for astronomical instruments for the 8.2m Subaru Telescope, for next generation 30 m class huge ground-based telescopes and for next generation large space-bone telescopes. We will also introduce a hybrid grism developed for MOIRCS (Multi-Object InfraRed Camera and Spectrograph) of the Subaru Telescope and a quasi-Bragg (QB) immersion grating. Test fabrication of B-VPH gratings with a liquid crystal (LC) of UV curable and normal LCs or a resin of visible light curable are performed. We successfully fabricated VB gratings of silicon as a mold with ridges of a high aspect ratio by means of the cycle etching process, oxidation and removal of silicon oxide. The RFT grating which is a surface-relief (SR) transmission grating with sawtooth shaped ridges of an acute vertex angle. The hybrid grism, as a prototype of the RFT grating, combines a high-index prism and SR transmission grating with sawtooth shape ridges of an acute vertex angle. The mold of the SR grating for the hybrid grism on to a work of Ni-P alloy of non-electrolysic plating successfully fabricated by using our ultra-precision machine and a single-crystal diamond bite. The QB immersion grating was fabricated by a combination of an inclined QB grating, Littrow prism and surface reflection mirror.
In 2014 and 2015 the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) instrument at the Subaru Telescope on Maunakea is underwent a significant modernization and upgrade project. We upgraded the two Hawaii2 detectors to Hawaii2-RG models, modernized the cryogenic temperature control system, and rewrote much of the instrument control software. The detector upgrade replaced the Hawaii2 detectors which use the Tohoku University Focal Plane Array Controller (TUFPAC) electronics with Hawaii2-RG detectors using SIDECAR ASIC (a fully integrated FPA controller system-on-a-chip) and a SAM interface card. We achieved an improvement in read noise by a factor of about 2 with this detector and electronics upgrade. The cryogenic temperature control upgrade focused on modernizing the components and making the procedures for warm up and cool down of the instrument safer. We have moved PID control loops out of the instrument control software and into Lakeshore model 336 cryogenic temperature controllers and have added interlocks on the warming systems to prevent overheating of the instrument. Much of the instrument control software has also been re-written. This was necessitated by the different interface to the detector electronics (ASIC and SAM vs. TUFPAC) and by the desire to modernize the interface to the telescope control software which has been updated to Subaru's "Gen2" system since the time of MOIRCS construction and first light. The new software is also designed to increase reliability of operation of the instrument, decrease overheads, and be easier for night time operators and support astronomers to use.
During the past year, the Multi-Object InfraRed Camera and Spectrograph at Subaru has undergone an upgrade of its science detectors, the housekeeping electronics and the instrument control software. This overhaul aims at increasing MOIRCS' sensitivity, observing efficiency and stability. Here we present the installation and the alignment procedure of the two Hawaii 2RG detectors and the design of a cryogenic focus mechanism. The new detectors show significantly lower read noise, increased quantum efficiency, and lower the readout time.
As a transmission grating, a surface-relief (SR) grating with sawtooth shaped ridges and volume phase holographic (VPH) grating are widely used for instruments of astronomical observations. However the SR grating is difficult to achieve high diffraction efficiency at high angular dispersion, and the VPH grating has low diffraction efficiency in high diffraction orders. We propose novel gratings that solve these problems. We introduce the hybrid grism which combines a high refractive index prism with a replicated transmission grating, which has sawtooth shaped ridges of an acute apex angle. The birefringence VPH (B-VPH) grating which contains an anisotropic medium, such as a liquid crystal, achieves diffraction efficiency up to 100% at the first diffraction order for natural polarization and for circular polarization. The quasi-Bragg (QB) grating which consists of long rectangular mirrors aligned in parallel precisely, like a window blind, achieves diffraction efficiency of 60% or more in higher than the 4th diffraction order. The volume binary (VB) grating with narrow grooves also achieves diffraction efficiency of 60% or more in higher than the 6th diffraction order. The reflector facet transmission (RFT) grating which is a SR grating with sawtooth shaped ridges of an acute apex angle achieves diffraction efficiency up to 80% in higher than the 4th diffraction order.
The project, "ULTIMATE- SUBARU", stands for "Ultra-wide Laser Tomographic Imager and MOS with AO for Transcendent Exploration at SUBARU Telescope." ULTIMATE-SUBARU provides a wide-field near infrared instrument at Cassegrain focus with GLAO. Performance simulation of GLAO at Subaru Telescope indicates that uniform PSFs can be obtained across the field of view up to 20 arcmin in diameter. This paper describes a current status of ULTIMATE-SUBARU project, science objectives, performance simulation update, system overview, feasibility of adaptive secondary mirror, and laser system.
An infrared instrument used for observation has to keep the detector and optical components in a very cold environment
during operation. However, because of maintenance, upgrades, and other routine work, there are situations that require
the instrument to be warmed-up and then cooled-down again. At Subaru Observatory, our MOIRCS infrared instrument
has required warm-up and cool-down several times a year for routine maintenance and filter replacement. The MOIRCS
instrument has a large heat capacity and cool-down using only the closed cycle cooler is impractical due to the huge
amount of time it would require. To address this problem Subaru engineers have created a mechanism to allow PRE-COOLING
of the instrument via liquid nitrogen - allowing for a much faster pre-cool process. Even with liquid nitrogen,
the pre-cool process requires 10 tanks and almost a week of continual monitoring in order to reach the desired target
temperature. It is very difficult to work for such a long period of time at the oxygen starved summit of Mauna Kea (4205
meters),and issues of man-power and scheduling conflicts only add to the problems. To address these concerns Subaru
developed an automated pre-cooling system which works continuously and remotely at the summit. The strategy was to
have basic functionality for pre-cooling and user friendly interface. i.e. (1) Continuous cooling until the target
temperature is reached by automated liquid nitrogen tank exchanges and precision temperature control by automated
changes to the liquid nitrogen flow. (2) Remote monitoring and control of all parameter setting by Web browser as user
interface (UI). The goal of the Subaru pre-cooling system was to make it both inexpensive and quick to implement by
using existing technologies. The original goal (to cut down on labor and precision temperature control) has been attained
through several pre-cooling and software/hardware modification cycles. We will report on the progress and status of our
pre-cooling experiences in this presentation.
The design, development, operation and current performance of MOS (multi-object spectroscopy) mode of MOIRCS is described. MOIRCS (Multi-Object Infrared Camera and Spectrograph) is one of the second-generation instruments for the Subaru Telescope and provides imaging and MOS modes with a 4' × 7' field of view for a wavelength range from 0.85 to 2.5 μm. To achieve near-infrared (NIR) MOS up to K-band, MOS mode uses multi-slit masks and a mask exchange system in a cryogenic environment. The masks are housed in a vacuum dewar attached to the MOIRCS main dewar and separated by a large gate valve. The mask dewar is equipped with its own cryogenic cooler and a vacuum pump and is capable of storing eighteen masks. The masks are made of thin aluminum foil. Slits are cut with a laser, with software that corrects for the effects of thermal contraction. The masks are cooled to below 130 K in the mask dewar and transported to the focal plane in the main dewar through the gate valve with a linear motion manipulator. An interlock is equipped on the mask exchange system to secure the cryogenic instrument from accident. Replacing masks can be done in the daytime without breaking the vacuum of the main dewar by isolating the mask dewar with the gate valve. Acquisition occurs by iteratively taking on-sky images through alignment holes on the mask until the rotation and offset between alignment stars and alignment holes become small enough. MOIRCS/MOS mode will be open to the public in late 2006.
MOIRCS is a new Cassegrain instrument of Subaru telescope, dedicated for wide field imaging and multi-object spectroscopy in near-infrared. MOIRCS has been constructed jointly by Tohoku University and the Subaru Telescope and saw the first light in Sept., 2004. The commissioning observations to study both imaging and spectroscopic performance were conducted for about one year. MOIRCS mounts two 2048 × 2048 HAWAII2 arrays and provides a field of view of 4' x 7' with a pixel scale of 0."117. All-lens optical design is optimized for 0.8 to 2.5 μm with no practical chromatic aberration. Observations confirm the high image quality over the field of view without any perceptible degradation even at the field edge. The best seeing we have obtained so far is FWHM=0."18. A novel design of MOIRCS enables us to perform multi-object spectroscopy with aluminum slit masks, which are housed in a carrousel dewar and cooled to ~ 110 K. When choosing MOS mode, a manipulator pulls out a slit mask from the carrousel into the MOIRCS main dewar and sets it properly at the Cassegrain focus. The carrousel is shuttered by a gate valve, so that it can be warmed and cooled independently to exchange slit-mask sets during daytime. We have tested various configurations of 30 or more multi-slit positions in various sky fields and found that targets are dropped at the centers of slits or guide holes within a dispersion of about 0.3 pixels (0."03). MOIRCS has been open to common use specifically for imaging observations since Feb. 2006. The MOS function will be available in next August.
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