SCALES is a 2 -5 micron, high-contrast, lenslet-based, integral field spectrograph (IFS) designed to characterize exoplanets and their atmospheres. In this proceeding, we present the updated design and current status of the SCALES slenslit, a novel take on an image slicer. The slenslit optics, which are being fabricated by Durham University’s Precision Optics group, dissect and rearrange a subset of lenslet micro-pupils into a pseudo-slit. The pseudo-slit is then dispersed with much higher spectral resolution than other lenslet-based IFS instruments. The slenslit technology opens new vistas for the characterization of exoplanet formation environments and atmospheres by improving the spectral resolution while maintaining the diffraction-limited imaging.
The SCALES instrument is a high-contrast imager and integral field spectrograph that operates in the infrared region and is intended to be utilized behind the W.M. Keck Observatory's adaptive optics system. The SCALES integral field spectrograph operates over a broad wavelength range from 2.0 to 5.0 µm. The instrument includes a microlens array-based integral field spectrograph that, when combined with a lenslet to slicer reformatter referred to as "slenslit," allows for low (R = 35 - 250) and moderate (R = 2000 - 6500) spectral resolution spectroscopy. We have done extensive end-to-end modeling of the SCALES optical path using both geometric optics and physical optics. This analysis has been vital in predicting both spectral format and optical performance. We have also combined the predicted geometric point spread function (PSF) given a complete end-to-end system including the SCALES lenslet array IFU, with modeled diffraction effects to understand the crosstalk between the spectra. The PSF modeling is being integrated with the SCALES instrument simulator to provide realistic data products that are being used to develop the SCALES data pipeline.
The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an under-construction thermal infrared high-contrast integral field spectrograph that will be located at the W. M. Keck Observatory. SCALES will detect and characterize planets that are currently inaccessible to detailed study by operating at thermal (2 μm to 5 μm) wavelengths and leveraging integral-field spectroscopy to readily distinguish exoplanet radiation from residual starlight. SCALES’ wavelength coverage and medium-spectral-resolution (R ∼ 4,000) modes will also enable investigations of planet accretion processes. We explore the scientific requirements of additional custom gratings and filters for incorporation into SCALES that will optimally probe tracers of accretion in forming planets. We use ray-traced hydrogen emission line profiles (i.e., Brγ, Brα) and the SCALES end-to-end simulator, scalessim, to generate grids of high-fidelity mock datasets of accreting planetary systems with varying characteristics (e.g., Teff, planet mass, planet radius, mass accretion rate). In this proceeding, we describe potential specialized modes that best differentiate accretion properties and geometries from the simulated observations.
The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is a 2 μm to 5 μm, high-contrast Integral Field Spectrograph (IFS) currently being built for Keck Observatory. With both low (R ≲ 250) and medium (R approximately 3500 to 7000) spectral resolution IFS modes, SCALES will detect and characterize significantly colder exoplanets than those accessible with near-infrared (approximately 1 μm to 2 μm) high-contrast spectrographs. This will lead to new progress in exoplanet atmospheric studies, including detailed characterization of benchmark systems that will advance the state of the art of atmospheric modeling. SCALES’ unique modes, while designed specifically for direct exoplanet characterization, will enable a broader range of novel (exo)planetary observations as well as galactic and extragalactic studies. Here we present the science cases that drive the design of SCALES. We describe an end-to-end instrument simulator that we use to track requirements and show simulations of expected science yields for each driving science case. We conclude with a discussion of preparations for early science when the instrument sees first light in approximately 2025.
High-contrast imaging has been used to discover and characterize dozens of exoplanets to date. The primary limiting performance factor for these instruments is contrast, the ratio of exoplanet to host star brightness that an instrument can successfully resolve. Contrast is largely determined by wavefront error, consisting of uncorrected atmospheric turbulence and optical aberrations downstream of AO correction. Single-point diamond turning allows for high-precision optics to be manufactured for use in astronomical instrumentation, presenting a cheaper and more versatile alternative to conventional glass polishing. This work presents measurements of wavefront error for diamond-turned aluminum optics in the Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument, a 2 micron to 5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. Wavefront error measurements for these optics are used to simulate SCALES’ point spread function using physical optics propagation software poppy, showing that SCALES’ contrast performance is not limited by wavefront error from internal instrument optics.
The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an Integral Field Spectrograph (IFS), under construction for W. M. Keck Observatory. It is optimized for 2 to 5-micron spectroscopy of exoplanets and also has a 1 to 5-micron imaging channel. As various optics arrive, we aim to validate their performances individually. In this paper, we present measurements and measurement techniques used to validate SCALES optics in the lab, including filter substrates, pupil masks for the cold stop and Lyot stops, neutral density filters, and diamond-turned mirrors.
The Santa cruz Extreme Adaptive optics (AO) laboratory (SEAL) testbed is designed to develop and prototype new technologies for high contrast imaging systems aimed at directly imaging exoplanets. SEAL consists of three deformable mirrors (DMs; segmented IrisAO, low-order ALPAO, and high order MEMS DMs), four pupil plane wavefront sensors (Shack-Hartman, two different Pyramid, and Zernike wavefront sensors), the FAST focal plane wavefront sensor, a suite of coronagraphs, and a CACAO based real-time-computer (RTC). Intending to test new AO control algorithms as well as compare new techniques with SEAL before implementing on-sky, we want to inject realistic atmospheric turbulence and study the effects of uncorrected high-order spatial modes in our system (e.g., the effects of aliasing and frequency folding on predictive control). To mimic continuous turbulence, as seen on-sky, we use a custom Meadowlark spatial light modulator (SLM). With a maximum stroke of 6pi (1.9um at 633 nm) and 1152x1920 pixels, we can simulate single layer turbulence with r0 of 11 cm and as well as reproduce the nominal conditions of r0>20cm on Mauna Kea. In this paper, we present the first results using our SLM to generate turbulence. We characterize the performance of the SLM by studying its spatial and temporal responses. We then show results with the different configurations SEAL enables with turbulence we inject using the SLM. We also provide practical information on the Python interface with SLM.
The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an instrument being designed to perform direct imaging of exoplanets in the mid-infrared (2-5 μm) with the Adaptive Optics System of W.M. Keck Observatory. To eliminate unwanted thermal infrared radiation, SCALES utilizes both a cold stop for excluding background radiation and a vector vortex coronagraph with Lyot stops for starlight suppression. Optimal geometric masks have been designed. We simulate the propagation of light through the Lyot plane and analyze the on-axis images of stars in the K, L, and M band for the performance of the Lyot stops. Additionally, finalized cold stop and Lyot stop designs are presented along with evaluations on the effects of manufacturing tolerances and tilt in pupil planes caused by off-axis parabolic mirror relays.
A next-generation instrument named, Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES), is being planned for the W. M. Keck Observatory. SCALES will have an integral field spectrograph (IFS) and a diffraction-limited imaging channel to discover and spectrally characterize the directly imaged exoplanets. Operating at thermal infrared wavelengths (1-5 μm, and a goal of 0.6-5 μm), the imaging channel of the SCALES is designed to cover a 12′′ × 12′′ field of view with low distortions and high throughput. Apart from expanding the mid-infrared science cases and providing a potential upgrade/alternative for the NIRC2, the H2RG detector of the imaging channel can take high-resolution images of the pupil to aid the alignment process. Further, the imaging camera would also assist in small field acquisition for the IFS arm. In this work, we present the optomechanical design of the imager and evaluate its capabilities and performances.
Astrophotonic technologies, specifically mass-produced “spectrometers-on-a-chip,” offer an exciting path toward dramatically reducing the cost-per-spectrum of astronomical spectrographs. This technology could one day enable significant multiplexing upgrades to fiber-based instruments and inspire new facilities capable of collecting 100,000 simultaneous spectra in both single-fiber and IFU formats. Here, we report on a new astrophotonics platform at Lick Observatory for on-sky testing of such technologies. Our initial focus is on the problem of efficiently coupling telescope light into photonic devices, which are typically optimized to work with a single mode, i.e., with diffraction-limited light. While photonic lanterns can deliver multiple single-mode outputs given multi-modal input, here we introduce the concept of Adaptive Mode Extraction (AME), which uses a second, reference lantern to select the brightest instantaneous mode or modes for injection into photonic devices. Analogous to “speckle spectroscopy,” this technique has the potential to increase the signal-to-noise ratio for faint sources by spatially filtering out the sky background. We have deployed our testing platform behind the AO system at the Shane Telescope and demonstrate that it meets requirements for our planned on-sky tests of AME, namely the ability to couple AO-corrected light from two nearby stars (within 2′′) into two dynamically-positioned lanterns, with adequate throughput (<40%) and image quality (0.15′′).
Liger is a second generation near-infrared imager and integral field spectrograph (IFS) for the W. M. Keck Observatory that will utilize the capabilities of the Keck All-sky Precision Adaptive-optics (KAPA) system. Liger operates at a wavelength range of 0.81 μm - 2.45 μm and utilizes a slicer and a lenslet array IFS with varying spatial plate scales and fields of view resulting in hundreds of modes available to the astronomer. Because of the high level of complexity in the raw data formats for the slicer and lenslet IFS modes, Liger must be designed in conjunction with a Data Reduction System (DRS) which will reduce data from the instrument in real-time and deliver science-ready data products to the observer. The DRS will reduce raw imager and IFS frames from the readout system and provide 2D and 3D data products via custom quick-look visualization tools suited to the presentation of IFS data. The DRS will provide the reduced data to the Keck Observatory Archive (KOA) and will be available to astronomers for offline post-processing of observer data. We present an initial design for the DRS and define the interfaces between observatory and instrument software systems.
The Fibre-Optic Broadband Spectrograph (FOBOS) is a facility-class multi-object spectrograph currently being designed, and to be deployed to the Keck II telescope. FOBOS is able to simultaneously observe 1729-objects across a 20′ field of view, with 30% instrument throughput from 0.31-1.0 µm and a spectral resolution of R<3500 delivered by three, bench-mounted 4-channel spectrographs. The FOBOS focal plane will be configured using 1729 ‘Starbug’ robots, which are vacuum-adhered piezo actuators that ‘walk’ across the field plate to position fibres. Using Starbugs to position fibres allows fast configuration and flexibility in payloads, with a mixture of Single Fibre, IFUs, and Imaging Bundles (used for guiding) capable of being rapidly positioned across the field. The FOBOS team have recently passed their conceptual design review. The FOBOS positioner design builds on the experience gained from the TAIPAN instrument, which used 150 Starbugs and demonstrated their viability as a science instrument. In this paper we detail the conceptual design of the FOBOS focal positioner system. This includes details of the Starbug design, optomechanics, and optical designs that allow the focal plane positioner to operate. The FOBOS focal positioner design builds on the experience gained from TAIPAN, a prototype instrument built to demonstrate the Starbugs technology
We present the design of SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) a new 2-5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. SCALES enables low-resolution (R∼50) spectroscopy, as well as medium-resolution (R∼4,000) spectroscopy with the goal of discovering and characterizing cold exoplanets that are brightest in the thermal infrared. Additionally, SCALES has a 12x12” field-of-view imager that will be used for general adaptive optics science at Keck. We present SCALES’s specifications, its science case, its overall design, and simulations of its expected performance. Additionally, we present progress on procuring, fabricating and testing long lead-time components.
SCALES (Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy) is a 2 - 5 micron high-contrast lenslet-based integral field spectrograph (IFS) designed to characterize exoplanets and their atmospheres. Like other lenslet-based IFSs, SCALES produces a short micro-spectrum of each lenslet’s micro-pupil. We have developed an image slicer that sits behind the lenslet array & dissects and rearranges a subset of micro-pupils into a pseudo-slit. The combination lenslet array and slicer (or slenslit) allows SCALES to produce much longer spectra, thereby increasing the spectral resolution by over an order of magnitude and allowing for comparisons to atmospheric modeling at unprecedented resolution. This proceeding describes the design and performance of the slenslit.
Liger is an adaptive optics (AO) fed imager and integral field spectrograph (IFS) designed to take advantage of the Keck All-sky Precision Adaptive-optics (KAPA) upgrade for the W.M. Keck Observatory. We present the design and analysis of the imager optical assembly including the spectrograph Re-Imaging Optics (RIO) which transfers the beam path from the imager focal plane to the IFS slicer module and lenslet array. Each imager component and the first two RIO mechanisms are assembled and individually aligned on the same optical plate. Baffling suppresses background radiation and scattered light, and a pupil viewing camera allows the imager detector to focus on an image of the telescope pupil. The optical plate mounts on an adapter frame for alignment of the overall system. The imager and RIO will be characterized in a cryogenic test chamber before installation in the final science cryostat.
The large distance between Earth and other planetary systems makes it so that exoplanets appear as point sources to our telescopes. This is in stark contrast to the appearance of our own solar system planets, which range in angular diameter from a few arcseconds to arcminutes. Their relatively large projected size on the sky allows for detailed analysis of planetary features such as rings, atmospheric and cloud features, and more. The Planet as Exoplanet Analog Spectrograph (PEAS) instrument at Lick Observatory is designed to simulate exoplanet observations and analysis techniques using disk integrated observations of the solar system planets. PEAS uses an integrating sphere to spatially scramble the light from the planet and take a spectrum of the entire visible surface. PEAS observations of solar system planets can then be used as benchmarks for testing and validating exoplanet observations and atmospheric models. In this work, we model the throughput of the PEAS instrument, including the telescope, integrating sphere, and spectrograph components. We are able to reproduce a PEAS spectrum to within a factor of 10. We then model the throughput with possible upgrades to the system and determine which new components would produce the best efficiency.
SCALES is a high-contrast, infrared coronagraphic imager and integral field spectrograph (IFS) to be deployed behind the W.M. Keck Observatory adaptive optics system. A reflective optical design allows diffraction-limited imaging over a large wavelength range (1.0 - 5.0 µm). A microlens array-based IFS coupled with a lenslet reformatter (”slenslit”) allow spectroscopy at both low (R = 35 - 250) and moderate (R = 2000 - 6500) spectral resolutions. The large wavelength range, diffraction-limited performance, high contrast coronagraphy and cryogenic operation present a unique optical design challenge. We present the full SCALES optical design, including performance modeling and analysis and manufacturing.
Liger is a next-generation near-infrared imager and integral field spectrograph (IFS) planned for the W.M. Keck Observatory. Liger is designed to take advantage of improved adaptive optics (AO) from the Keck All-Sky Precision Adaptive Optics (KAPA) upgrade currently underway. Liger operates at 0.84-2.45 µm with spectral resolving powers of R∼4,000-10,000. Liger makes use of a sequential imager and spectrograph design allowing for simultaneous observations. There are two spectrograph modes: a lenslet with high spatial sampling of 14 and 31 mas, and a slicer with 75 and 150 mas sampling with an expanded field of view. Two pick-off mirrors near the imager detector direct light to these two IFS channels. We present the design and structural analysis for the imager detector and IFS pick-off mirror mounting assembly that will be used to align and maintain stability throughout its operation. A piezoelectric actuator will be used to step through 3 mm of travel during alignment of the instrument to determine the optimal focus for both the detector and pick-off mirrors which will be locked in place during normal operation. We will demonstrate that the design can withstand the required gravitational and shipping loads and can be aligned within the positioning tolerances for the optics.
Since the start of science operations in 1993, the twin 10-meter W. M. Keck Observatory (WMKO) telescopes have continued to maximize their scientific impact and to produce transformative discoveries that keep the observing community on the frontiers of astronomical research. Upgraded capabilities and new instrumentation are provided though collaborative partnerships with Caltech, the University of California, and the University of Hawaii instrument development teams, as well as industry and other organizations. This paper summarizes the performance of recently commissioned infrastructure projects, technology upgrades, and new additions to the suite of observatory instrumentation. We also provide a status of projects currently in design or development phases and, since we keep our eye on the future, summarize projects in exploratory phases that originate from our 2022 strategic plan developed in collaboration with our science community to adapt and respond to evolving science needs.
Liger is a next-generation near-infrared (810 - 2450 nm) integral field spectrograph (IFS) and imaging camera for the Keck Observatory adaptive optics (AO) system. Liger will enable new science by providing enhanced capabilities, including higher spectral resolving power (R=4,000 – 10,000), access to shorter wavelengths (< 1000 nm), and larger fields of view (13 arcsec x 7 arcsec) than any current or planned ground- or space-based IFS system. The imaging camera sequentially feeds an IFS that makes use of slicer assembly unit and lenslet array. We will present the overall design of the Liger subsystems and review the key science drivers.
We describe the current plans for developing an adaptive secondary mirror-based (ASM) adaptive optics (AO) system for WMKO. An ASM allows for the integration of AO into the telescope itself, broadening use of AO to include wide-field enhanced seeing, high contrast observations, and enabling future multi-conjugate upgrades. Such a system has the potential for enhancing a range of science objectives, improving the performance of both existing and future instrumentation at Keck. We describe a system level ASM-AO concept based on hybrid variable reluctance actuators, developed by TNO that simplifies the implementation of ASM’s.
The Santa Cruz Extreme AO Lab (SEAL) is a new visible-wavelength testbed designed to advance the state of the art in wavefront control for high contrast imaging on large, segmented, ground-based telescopes. SEAL provides multiple options for simulating atmospheric turbulence, including a custom spatial light modulator. A 37-segment deformable mirror simulates the W. M. Keck Observatory segmented primary mirror. The adaptive optics system consists of a woofer/tweeter DM system, and four wavefront sensor arms: 1) a high-speed Shack-Hartmann WFS, 2) a reflective pyramid WFS, 3) vector-Zernike mask, and 4) a Fast Atmospheric SCC Technique demonstration arm. Finally, a science arm preliminarily includes a classical Lyot-style coronagraph. SEAL's real time control system is based on the CACAO package, and is designed to support the efficient transfer of software between SEAL and the Keck II AO system. In this paper, we present an overview of the design and first light performance of SEAL.
IRIS (Infrared Imaging Spectrograph) is the near-infrared (0.84 to 2.4 micron) diffraction-limited imager and Integral Field Spectrograph (IFS) designed for the Thirty Meter Telescope (TMT) and the Narrow-Field Infrared Adaptive Optics System ( NFIRAOS ). The imager will have a 34 arcsec x 34 arcsec field of view with 4 milliarcseconds (mas) pixels. The IFS consists of a lenslet array and slicer, enabling four plate scales from 4 mas to 50 mas, with multiple gratings and filters. We will report the progress on the development of the IRIS Data Reduction System ( DRS ) in the final design phase. The IRIS DRS is being developed in Python with the software architecture based on the James Webb Space Telescope science calibration pipeline. We are developing a library of algorithms as individual Python classes that can be configured independently and bundled into pipelines. We will interface this with the observatory software to run online during observations and we will release the package publicly for scientists to develop custom analyses. It also includes a C library for readout processing to be used for both in real-time processing (e.g., up-the-ramp, MCDS) as well the ability for astronomers to use for offline reduction. Lastly, we will also discuss the development of the IRIS simulation packages that simulate raw spectra and image readout-data from the Hawaii-4RG detectors, which helps in developing reduction algorithms during this design phase.
The TMT Early-Career Initiative (TECI) is an innovative, evolving program designed to support inclusion in the Thirty Meter Telescope (TMT) International Observatory (TIO) by engaging graduate students and postdocs in TIO projects, and preparing them with skills required to contribute to the project and advance in their careers. TECI has an annual cycle that begins with a workshop that includes project management, instrument design, and teamwork sessions, and engages participants in projects that could lead to visits and new collaborations. Project teams are led by the participants themselves, who consult with a member of the relevant technical team or project staff. In this paper we describe the components of TECI, our approach to designing it, and outcomes from our early piloting in 2016-17, as well as our first full program in 2018-19.
An Adaptive secondary mirror (ASM) allows for the integration of adaptive optics (AO) into the telescope itself. Adaptive secondary mirrors, based on hybrid variable reluctance (HVR) actuator technology, developed by TNO, provide a promising path to telescope-integrated AO. HVR actuators have the advantage of allowing mirrors that are sti↵er, more power ecient, and potentially less complex than similar, voice-coil based ASM’s. We are exploring the application of this technology via a laboratory testbed that will validate the technical approach. In parallel, we are developing conceptual designs for ASMs at several telescopes including the Automated Planet Finder Telescope (APF) and for Keck Observatory. An ASM for APF has the potential to double the light through the slit for radial velocity measurements, and dramatically improved the image stability. An ASM for WMKO enables ground layer AO correction and lower background infrared AO observations, and provides for more flexible deployment of instruments via the ability to adjust the location of the Cassegrain focus.
SCALES (Santa Cruz Array of Lenslets for Exoplanet Spectroscopy) is a 2-5 micron high-contrast lenslet integral-field spectrograph (IFS) driven by exoplanet characterization science requirements and will operate at W. M. Keck Observatory. Its fully cryogenic optical train uses a custom silicon lenslet array, selectable coronagraphs, and dispersive prisms to carry out integral field spectroscopy over a 2.2 arcsec field of view at Keck with low (< 300) spectral resolution. A small, dedicated section of the lenslet array feeds an image slicer module that allows for medium spectral resolution (5000 10000), which has not been available at the diffraction limit with a coronagraphic instrument before. Unlike previous IFS exoplanet instruments, SCALES is capable of characterizing cold exoplanet and brown dwarf atmospheres (< 600 K) at bandpasses where these bodies emit most of their radiation while capturing relevant molecular spectral features.
Starbugs are robotic devices that have the capability to simultaneously position many optical fibers, over the telescope’s focal plane to carry-out efficient spectroscopic surveys. The conceptual design of FOBOS, the Fiber-Optic Broadband Optical Spectrograph, deploys Starbugs at the Keck II focal plane to enable high-multiplex, deep spectroscopic follow-up of upcoming deep-imaging surveys. FOBOS requires configured fields of many-hundreds of targets (significantly more than TAIPAN and MANIFEST instruments) in a few minutes, consistent with typical detector readout times. FOBOS also requires the inclusion of different optical payloads, like integral field-units, calibration bundles, coherent imaging bundles and perhaps wavefront sensors. Therefore, with these new challenges, it is important to optimize the target allocation and routing algorithms for Starbugs that yield the best configuration times and science outcomes for FOBOS. We provide a description of the Starbug parameters required by the FOBOS conceptual design, perform relevant allocation simulations, and discuss their performance.
Spectrographs are integral in panoramic surveys. An optimized spectrograph design can facilitate the observation of faint objects. One such optimization lies in its bundle of optical fibers and their numerical apertures (NA). Low NA fibers are less commonly used and studied, but can be advantageous in terms of cost and precision. Here, we describe the properties of 0.12 NA and 0.22 NA fibers with different input beam f-ratio, quantities of wraps, and bend radii.
Liger is a next-generation near-infrared imager and integral field spectrograph (IFS) for the W.M. Keck Obser- vatory designed to take advantage of the Keck All-Sky Precision Adaptive Optics (KAPA) upgrade. Liger will operate at spectral resolving powers between R~4,000 - 10,000 over a wavelength range of 0.8-2.4µm. Liger takes advantage of a sequential imager and spectrograph design that allows for simultaneous observations between the two channels using the same filter wheel and cold pupil stop. We present the design for the filter wheels and pupil mask and their location and tolerances in the optical design. The filter mechanism is a multi-wheel de- sign drawing from the heritage of the current Keck/OSIRIS imager single wheel design. The Liger multi-wheel configuration is designed to allow future upgrades to the number and range of filters throughout the life of the instrument. The pupil mechanism is designed to be similarly upgradeable with the option to add multiple pupil mask options. A smaller wheel mechanism allows the user to select the desired pupil mask with open slots being designed in for future upgrade capabilities. An ideal pupil would match the shape of the image formed of the primary and would track its rotation. For different pupil shapes without tracking we model the additional exposure time needed to achieve the same signal to noise of an ideal pupil and determine that a set of fixed masks of different shapes provides a mechanically simpler system with little compromise in performance.
We will present the status of the next generation near-infrared (0.84 - 2.45 micron) imager and integral field spectrograph (IFS) instrument, Liger, that is being designed for the W. M. Keck Observatory. The Liger imager and IFS operates concurrently on-sky and are optimized to sample the Keck All-sky Precision Adaptive optics (KAPA) system. The Liger IFS design is able to offer new science capabilities by extending to bluer wavelength coverage, larger field of views, and range of spectral resolving powers. We will discuss the overall Liger technical design, science requirements, and implementation plans for the entire program.
IRIS is a diffraction limited instrument designed for first light of the Thirty Meter Telescope (TMT). It combines a nearinfrared integral field spectrograph (lenslet array and mirror slicer) and a wide-field imager with platescales as small as 4 mas. The project is nearing the end of its final design phase and will soon be ready for fabrication. Our team has created a wide variety of prototypes and design solutions for this advanced instrument. While many challenges like atmospheric dispersion correction and saturation are particularly acute due to the telescope diameter, many others arise from the large format detector arrays and wide range of science goals. We’ll present the overall design, results from our prototyping activities and discuss the astrophysical opportunities.
The Fiber Optic Broad-band Optical Spectrometer (FOBOS) is a high-priority spectroscopic facility concept for the W. M. Keck Observatory. Here, we provide an update on the FOBOS conceptual design. FOBOS will deploy 1800 fibers across the 20-arcminute field-of-view of the Keck II Telescope. Starbugs fiber positioners will be used to deploy individual fibers as well as fiber-bundle arrays (integral field units, IFUs). Different combinations of active single fibers or IFUs can be selected to carry light to one of three mounted spectrographs, each with a 600-fiber pseudoslit. Each spectrograph has four wavelength channels, enabling end-to-end instrument sensitivity greater than 30% from 0.31-1.0 µm at a spectral resolution of R ~ 3500. With its high fiber density on a large telescope and modest field-of-view, FOBOS is optimized to obtain deep spectroscopy for large samples. In single- fiber mode, it will deliver premier spectroscopic reference sets for maximizing the information (e.g., photometric redshifts) that can be extracted from panoramic imaging surveys obtained from the forthcoming Rubin and Roman Observatories. Its IFUs will map emission from the circumgalactic interface between forming galaxies and the intergalactic medium at z ~ 2–3, and lay the path for multiplexed resolved spectroscopy of high-z galaxies aided by ground-layer and multi-object adaptive optics. In the nearby universe, its high sampling density and combination of single-fiber and IFU modes will revolutionize our understanding of the M31 disk and bulge via stellar populations and kinematics. Finally, with a robust and intelligent target and program allocation system, FOBOS will be a premier facility for follow-up of rare, faint, and transient sources that can be interleaved into its suite of observing programs. With a commitment to delivering science-ready data products, FOBOS will enable unique and powerful combinations of focused, PI-led programs and community-driven observing campaigns that promise major advances in cosmology, galaxy formation, time-domain astronomy, and stellar evolution.
Liger is a next generation adaptive optics (AO) fed integral field spectrograph (IFS) and imager for the W. M. Keck Observatory. This new instrument is being designed to take advantage of the upgraded AO system provided by Keck All-Sky Precision Adaptive-optics (KAPA). Liger will provide higher spectral resolving power (R~4,000- 10,000), wider wavelength coverage ( 0.8-2.4 µm), and larger fields of view than any current IFS. We present the design and analysis for a custom-made dewar chamber for characterizing the Liger opto-mechanical system. This dewar chamber is designed to test and assemble the Liger imaging camera and slicer IFS components while being adaptable for future experiments. The vacuum chamber will operate below 10−5 Torr with a cold shield that will be kept below 90 K. The dewar test chamber will be mounted to an optical vibration isolation platform and further isolated from the cryogenic and vacuum systems with bellows. The cold head and vacuums will be mounted to a custom cart that will also house the electronics and computer that interface with the experiment. This test chamber will provide an efficient means of calibrating and characterizing the Liger instrument and performing future experiments.
We present the optical design of the Red arm (operating at 2-5 µm) of the Planetary Systems Imager (PSI). At the heart of this arm of PSI is a 180x180 silicon lenslet array which will allow diffraction-limited low- resolution integral field spectroscopy over a field of view of 1.5 arcseconds on the Thirty Meter Telescope. The entrance window, lenslet array, and dispersing prisms are the only refractive optics; all other optics are diamond-turned, off-axis, aspherical, gold-coated aluminum and designed with a ‘bolt-and-go’ opto-mechanical approach. We use a homologous material design, meaning we have guaranteed exquisite coefficient of thermal expansion matching which allows us to test, align, and adjust the optics (apart from the lenslet array) in ambient laboratory conditions. Several ‘plug-and-play’ upgrades that increase the scientific capabilities of the instrument are also included in the design such that they can be integrated into the instrument at a later stage without much rework and redesign required. A novel upgrade is an image slicer that sits behind the lenslet array and is illuminated with an insertable fold mirror; this allows us to boost the spectral resolution to 2000-10000 for a field of view of 0.15x0.15 square arcseconds depending on the bandpass. This is a new realm of spectral resolution with ‘large field of view’ IFU instrumentation at these wavelengths and present a novel opportunity for exoplanet characterization. This hybrid lenslet/image slicer combination trades spatial coverage for vastly increased spectral resolution by geometrically rearranging a subset of 23x23 lenslets into a pseudo-slit which is then dispersed using selectable 1st order gratings.
The Wide Field Optical Spectrometer (WFOS) is a seeing limited, multi-object spectrograph and first light instrument for the Thirty Meter Telescope (TMT) scheduled for first observations in 2027. The spectrograph will deliver a minimum resolution of R~5,000 over a simultaneous wavelength range of 310 nm to 1,000 nm with a multiplexing goal of between 20 and 700 targets. The WFOS team consisting of partners in China, India, Japan, and the United States has completed a trade study of two competing concepts intended to meet the design requirements derived from the WFOS detailed science case. The first of these design concepts is a traditional slit mask instrument capable of delivering R~1,000 for up to 100 simultaneous targets using 1 x 7 arc second slits, and a novel focal plane slicing method for R~5,000 on up to 20 simultaneous targets can be achieved by reformatting the 1 arc-second wide slits into three 0.3 arc-second slits projected next to each other in the spatial direction. The second concept under consideration is a highly multiplexed fiber based system utilizing a robotic fiber positioning system at the focal plane containing 700 individual collectors, and a cluster of up to 12 replicated spectrographs with a minimum resolution of R~5,000 over the full pass band. Each collecting element will contain a bundle of 19 fibers coupled to micro-lens arrays that allow for contiguous coverage of targets and adaptation of the f/15 telescope beam to f/3.2 for feeding the fiber system. This report describes the baseline WFOS design, provides an overview of the two trade study concepts, and the process used to down-select between the two options. Also included is a risk assessment regarding the known technical challenges in the selected design concept.
With the successful completion of our preliminary design phase, we will present an update on all design aspects of the IRIS near-infrared integral field spectrograph and wide-field imager for the Thirty Meter Telescope (TMT). IRIS works with the Narrow Field Infrared Adaptive Optics System (NFIRAOS) to make observations at the diffraction limit of TMT at wavelengths between 0.84 and 2.4 microns. The imager has been expanded to a 34 arcsec field of view and the spectrograph has a wide range of filter and spectral format combinations with a contiguous field of view up to 112x128 spatial elements. Among the many challenges the instrument faces, and has tried to address in its design, are atmospheric dispersion up to 100 times the sampling scale, unprecedented saturation issues in crowded fields, and the need for integrated on-instrument wavefront sensors. But the scientific payoff is enormous and IRIS on TMT will open entirely new opportunities in all areas of astrophysical science.
TMT’s wide field optical spectrograph is a multi-object, first-light instrument with broad continuous wavelength coverage (0.310 – 1.0 m) at a moderate spectral resolution of R = 5000. The international WFOS design team has recently completed the downselect of two design approaches: a slicer-based monolithic architecture and a fiber-based modular concept. We present here the end-to-end conceptual design for the fiber-based optical spectrograph. Included are the front-end focal reduction optics for coupling light into the fibers, the spectrograph collimator and camera optics, and the dispersive architecture for each color channel. The highly multiplexed fiber-WFOS presents a unique design challenge in keeping costs for the modular spectrographs low while maintaining performance gains afforded by the TMT, and in particular the TMT plus ground-layer adaptive optics (GLAO). A full performance analysis including predicted spectral resolution and throughput is presented for the design.
We present a review of the ongoing research activity surrounding the adaptive optics system at the Shane telescope (ShaneAO) particularly the R&D efforts on the technology and algorithms for that will advance AO into wider application for astronomy. We are pursuing the AO challenges for whole sky coverage diffraction-limited correction down to visible science wavelengths. This demands high-order wavefront correction and bright artificial laser beacons. We present recent advancements in the development of MEMS based AO correction, woofer-tweeter architecture, wind-predictive wavefront control algorithms, atmospheric characterization, and a pulsed fiber amplifier guide star laser tuned for optical pumping of the sodium layer. We present the latest on-sky results from the new AO system and present status and experimental plans for the optical pumping guide star laser.
The Lick Observatory's Shane 3-meter telescope has been upgraded with a new infrared instrument (ShARCS - Shane Adaptive optics infraRed Camera and Spectrograph) and dual-deformable mirror adaptive optics (AO) system (ShaneAO). We present first-light measurements of imaging sensitivity in the Ks band. We compare mea- sured results to predicted signal-to-noise ratio and magnitude limits from modeling the emissivity and throughput of ShaneAO and ShARCS. The model was validated by comparing its results to the Keck telescope adaptive optics system model and then by estimating the sky background and limiting magnitudes for IRCAL, the pre- vious infra-red detector on the Shane telescope, and comparing to measured, published results. We predict that the ShaneAO system will measure lower sky backgrounds and achieve 20% higher throughput across the JHK bands despite having more optical surfaces than the current system. It will enable imaging of fainter objects (by 1-2 magnitudes) and will be faster to reach a fiducial signal-to-noise ratio by a factor of 10-13. We highlight the improvements in performance over the previous AO system and its camera, IRCAL.
It is possible to create custom laser guidestar (LGS) asterisms from a single beam by using a deformable mirror to pattern the phase of the outgoing laser guidestar beam. This avoids the need for multiple laser launch assemblies, and in principle would allow one to position the multiple LGS spots in any desired arrangement around the science target, as well as dynamically rotate the LGS pattern on-sky and control the distribution of intensity in each spot. Simulations and laboratory experiments indicate that a PTT111 and PTT489 IrisAO MEMS deformable mirror and a Hamamatsu X8267 spatial light modulator may have applications for creating small LGS asterisms for biological imaging with adaptive optics. For astronomy applications, the phase values required to
produce the “3+1” laser guidestar asterism of Keck’s Next Generation AO system is also
investigated.
Fluorides are useful low-index materials that can be used to enhance reflectivity of over-coated metallic films. In particular, YF3 has been suggested as a useful low-stress low-index material in the IR where film layers must be thicker, and it has also been found to enhance durability in silver-based mirrors. However, if these mirrors need to be stripped for recoating, care must be taken with the stripping process to avoid damaging a silica-based substrate through production of hydrofluoric acid. We present data that such damage can occur, and discuss empirically-derived alternative stripping processes in place of the normal acid-based approach to mitigate the danger.
A Cassegrain mounted adaptive optics instrument presents unique challenges for opto-mechanical design. The flexure and temperature tolerances for stability are tighter than those of seeing limited instruments. This criteria requires particular attention to material properties and mounting techniques. This paper addresses the mechanical designs developed to meet the optical functional requirements. One of the key considerations was to have gravitational deformations, which vary with telescope orientation, stay within the optical error budget, or ensure that we can compensate with a steering mirror by maintaining predictable elastic behavior. Here we look at several cases where deformation is predicted with finite element analysis and Hertzian deformation analysis and also tested. Techniques used to address thermal deformation compensation without the use of low CTE materials will also be discussed.
The identification and prediction of time-varying wavefront errors in adaptive optics (AO) systems promises fainter limiting
guide star magnitudes and improved temporal bandwidth errors. In a new UCSC-LLNL collaboration, we aim to demonstrate
the power of predictive Fourier controllers for AO in the laboratory and on-sky. We have used the Fourier Wind
Identification technique to measure wind velocities at several telescopes, and now have demonstrated the identification of
frozen flow turbulence with a translating phase screen on a laboratory test bench.
Here, we present identification of the wind direction and velocity using telemetry data from a laboratory testbed simulating
the ShaneAO system geometry. Our wind identification system uses a Fourier decomposition technique to identify
the correlated movement of the atmosphere from WFS telemetry data, which are then used to construct a Kalman filter for
real-time operation. We demonstrate the use of an LQG controller with the ShaneAO system architecture, and show that
the effects of frozen flow turbulence can be easily identified in laboratory telemetry. We describe the adaptations made
to the LQG controller to integrate it into the dual-DM architecture of the ShaneAO system, and demonstrate that these
modifications produce stable and well-understood AO correction in the laboratory.
A new high-order adaptive optics system is now being commissioned at the Lick Observatory Shane 3-meter telescope in California. This system uses a high return efficiency sodium beacon and a combination of low and high-order deformable mirrors to achieve diffraction-limited imaging over a wide spectrum of infrared science wavelengths covering 0.8 to 2.2 microns. We present the design performance goals and the first on-sky test results. We discuss several innovations that make this system a pathfinder for next generation AO systems. These include a unique woofer-tweeter control that provides full dynamic range correction from tip/tilt to 16 cycles, variable pupil sampling wavefront sensor, new enhanced silver coatings developed at UC Observatories that improve science and LGS throughput, and tight mechanical rigidity that enables a multi-hour diffraction-limited exposure in LGS mode for faint object spectroscopy science.
By inserting a MEMS deformable mirror-based adaptive optics system into the beam transfer optics of the Shane 3-meter telescope at Mt. Hamilton, we actively controlled the wavefront of the outgoing sodium laser guidestar beam. It was possible to show that a purposefully aberrated beam resulted in poorer performance of the Adaptive Optics system located behind the primary, though bad seeing conditions prevented us from improving the system’s performance over its nominal state. A silver-coated Iris AO deformable mirror was subjected to approximately 9.5 hours of exposure to a sodium laser guidestar of 3.5 Watts average output power and showed no signs of permanent damage or degradation in performance. Future applications of the uplink-AO system for correcting atmospheric turbulence and in generating custom laser guidestar asterisms are also discussed.
We describe the design and first-light early science performance of the Shane Adaptive optics infraRed Camera- Spectrograph (ShARCS) on Lick Observatory’s 3-m Shane telescope. Designed to work with the new ShaneAO adaptive optics system, ShARCS is capable of high-efficiency, diffraction-limited imaging and low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a HAWAII-2RG infrared detector, giving high quantum efficiency (<80%) and Nyquist sampling the diffraction limit in all three wavelength bands. The ShARCS instrument is also equipped for linear polarimetry and is sensitive down to 650 nm to support future visible-light adaptive optics capability. We report on the early science data taken during commissioning.
We evaluate the performance of a woofer-tweeter controller architecture for the new 3-meter Shane Telescope (Lick Observatory) laser guidestar adaptive optics (AO) system. Low order, high stroke phase correction is performed using the normal modal basis set of the Alpao woofer deformable mirror (DM). Since the woofer and tweeter DMs share the same wavefront sensor, the projected woofer phase correction is offloaded from the high-order, low stroke phase aberrations corrected by the tweeter DM. This ensures the deformable mirrors complementarily correct the input phase disturbance and minimizes likelihood of the tweeter actuators saturating. Preliminary analysis of on-sky closed-loop deformable mirror telemetry data from currently operating AO systems at Mt. Hamilton, as well as statistically accurate Kolmogorov phase screens, indicate that correction of up to 34 woofer modes results in all tweeter actuators remaining within their stroke limit.
The Lick Observatory 3-meter telescope has a history of serving as a testbed for innovative adaptive optics techniques.
In 1996, it became one of the first astronomical observatories to employ laser guide star (LGS) adaptive optics as a
facility instrument available to the astronomy community. Work on a second-generation LGS adaptive optics system,
ShaneAO, is well underway, with plans to deploy on telescope in 2013. In this paper we discuss key design features and
implementation plans for the ShaneAO adaptive optics system. Once again, the Shane 3-m will host a number of new
techniques and technologies vital to the development of future adaptive optics systems on larger telescopes. Included is a
woofer-tweeter based wavefront correction system incorporating a voice-coil actuated, low spatial and temporal
bandwidth, high stroke deformable mirror in conjunction with a high order, high bandwidth MEMs deformable mirror.
The existing dye laser, in operation since 1996, will be replaced with a fiber laser recently developed at Lawrence
Livermore National Laboratories. The system will also incorporate a high-sensitivity, high bandwidth wavefront sensor
camera. Enhanced IR performance will be achieved by replacing the existing PICNIC infrared array with an Hawaii
2RG. The updated ShaneAO system will provide opportunities to test predictive control algorithms for adaptive optics.
Capabilities for astronomical spectroscopy, polarimetry, and visible-light adaptive optical astronomy will be supported.
We explore the extension of predictive control techniques to multi-guide star, multi-layer tomographic wavefront
measurement systems using a shift-and-average correction scheme that incorporates wind velocity and direction. In
addition to reducing temporal error budget terms, there are potentially additional benefits for tomographic AO systems;
the combination of wind velocity information and phase height information from multiple guide stars breaks inherent
degeneracies in volumetric tomographic reconstruction, producing a reduction in the geometric tomographic error. In a
tomographic simulation of an 8-meter telescope with 3 laser guide stars over 2 arcminute diameter, we find that tracking
organized wind motion as it flows into metapupil regions sampled by only one guide star improves layer estimates
beyond the guide star radius, allowing for an expansion of the field of view. For this case, we demonstrate improvement
of layer phase estimates of 3% to 12%, translating into potential gains in the MOAO field of regard area of up to 40%.
The majority of the benefits occur in regions of the metapupil sampled by only 1-2 LGS's downwind at high altitudes.
We report on the preliminary design of W.M. Keck Observatory's (WMKO's) next-generation adaptive optics (NGAO)
facility. This facility is designed to address key science questions including understanding the formation and evolution
of today's galaxies, measuring dark matter in our galaxy and beyond, testing the theory of general relativity in the
Galactic Center, understanding the formation of planetary systems around nearby stars, and exploring the origins of our
own solar system. The requirements derived from these science questions have resulted in NGAO being designed to
have near diffraction-limited performance in the near-IR (K-Strehl ~ 80%) over narrow fields (< 30" diameter) with
modest correction down to ~ 700 nm, high sky coverage, improved sensitivity and contrast and improved photometric
and astrometric accuracy. The resultant key design features include multi-laser tomography to measure the wavefront
and correct for the cone effect, open loop AO-corrected near-IR
tip-tilt sensors with MEMS deformable mirrors (DMs)
for high sky coverage, a high order MEMS DM for the correction of atmospheric and telescope static errors to support
high Strehls and high contrast companion sensitivity, point spread function (PSF) calibration to benefit quantitative
astronomy, a cooled science path to reduce thermal background, and a high-efficiency science instrument providing
imaging and integral field spectroscopy.
KEYWORDS: Mirrors, Imaging systems, Adaptive optics, Iterated function systems, Sensors, Spectrographs, Signal to noise ratio, Point spread functions, Telescopes, Relays
In this paper we report on the preliminary design of DAVINCI, the first light science instrument for the W. M. Keck
Observatory's Next Generation Adaptive Optics facility. DAVINCI will provide imaging and coronagraphy at the
diffraction limit from 0.7 μm to 2.4 μm over a field of ~30", and integral field spectroscopy with three sampling scales
(10, 35, and 50 mas) and a field of view of 5.6" x 3" for the largest (50 mas) sampling scale. The science requirements
for DAVINCI are discussed, followed by an examination of the challenges of designing the instrument within a strict
limit on overall cost. The instrument's optical design and opto-mechanical configuration is described as well as the
current performance predictions for the instrument.
A critical goal in the next decade is to develop techniques that will extend Adaptive Optics correction to visible
wavelengths on Extremely Large Telescopes (ELTs). We demonstrate in the laboratory the highly accurate atmospheric
tomography necessary to defeat the cone effect on ELTs, an essential milestone on the path to this capability. We
simulate a high-order Laser Tomographic AO System for a 30-meter telescope with the LTAO/MOAO testbed at UCSC.
Eight Sodium Laser Guide Stars (LGSs) are sensed by 99x99 Shack-Hartmann wavefront sensors over 75". The AO
system is diffraction-limited at a science wavelength of 800 nm
(S ~ 6-9%) over a field of regard of 20" diameter. Openloop
WFS systematic error is observed to be proportional to the total input atmospheric disturbance and is nearly the
dominant error budget term (81 nm RMS), exceeded only by tomographic wavefront estimation error (92 nm RMS).
The total residual wavefront error for this experiment is comparable to that expected for wide-field tomographic adaptive
optics systems of similar wavefront sensor order and LGS constellation geometry planned for Extremely Large
Telescopes.
W. M. Keck Observatory (WMKO) is currently engaged in the design of a powerful new Adaptive Optics (AO) science
capability providing precision correction in the near-IR, good correction in the visible, and faint object multiplexed
integral field spectroscopy. Improved sensitivity will result from significantly higher Strehl ratios over narrow fields (<
30" diameter) and from lower backgrounds. Quantitative astronomy will benefit from improved PSF stability and
knowledge. Strehl ratios of 15 to 25% are expected at wavelengths as short as 750 nm. A multi-object AO approach
will be taken for the correction of multiple science targets over modest fields of regard (< 2' diameter) and to achieve
high sky coverage using AO compensated near-IR tip/tilt sensing. In this paper we present the conceptual design for this
system including discussion of the requirements, system architecture, key design features, performance predictions and
implementation plans.
We have demonstrated MOAO-type atmospheric compensation on a 10 meter telescope at visible wavelengths with the
UCO/Lick MCAO/MOAO testbed in the Laboratory for Adaptive Optics at UCSC. We report Strehls of ~20% in R
band (658 nm) on-axis and Strehls of ~15% off-axis 25" for a 3D Mauna Kea-type atmosphere with r0 = 15 cm and &Tgr;0 =
3.5". We show that a tomographic MOAO approach with 5 LGS's in a 50" constellation is sufficient to realize good
correction in the visible. Two major improvements to the testbed realized this gain: (1) An upgrade to 64x64
subapertures across a 10 meter pupil (2) and a predictor-corrector wind model. We discuss limitations to wide-field
visible light AO on 8-10 meter class telescopes and stress that the tomographic error due to blind modes is frequently the
largest field-dependent error. We use a predictor-corrector wind model (Wiberg et al. 2006) to take advantage of windlayer
shearing in the atmosphere to reduce the tomographic error over a 50" diameter field. Depending on the validity of
the Taylor frozen flow model for individual layers in the real atmosphere, this approach could be more effective than
increasing the number of LGS's.
The Next Generation Adaptive Optics (NGAO) system will represent a considerable advancement for high resolution
astronomical imaging and spectroscopy at the W. M. Keck Observatory. The AO system will incorporate multiple laser
guidestar tomography to increase the corrected field of view and remove the cone effect inherent to single laser guide
star systems. The improvement will permit higher Strehl correction in the near-infrared and diffraction-limited correction
down to R band. A high actuator count micro-electromechanical system (MEMS) deformable mirror will provide the
on-axis wavefront correction to a number of instrument stations and additional MEMS devices will feed multiple
channels of a deployable integral-field spectrograph. In this paper we present the status of the AO system design and
describe its various operating modes.
We investigate the non-modulating pyramid wave-front sensor's (P-WFS) implementation in the context of Lick
Observatory's Villages visible light AO system on the Nickel 1-meter telescope. A complete adaptive optics correction,
using a non-modulated P-WFS in slope sensing mode as a boot-strap to a regime in which the P-WFS can act as a direct
phase sensor is explored. An iterative approach to reconstructing the wave-front phase, given the pyramid wave-front
sensor's non-linear signal, is developed. Using Monte Carlo simulations, the iterative reconstruction method's photon
noise propagation behavior is compared to both the pyramid sensor used in slope-sensing mode, and the traditional
Shack Hartmann sensor's theoretical performance limits. We determine that bootstrapping using the P-WFS as a slope
sensor does not offer enough correction to bring the phase residuals into a regime in which the iterative algorithm can
provide much improvement in phase measurement. It is found that both the iterative phase reconstructor and the slope
reconstruction methods offer an advantage in noise propagation over Shack Hartmann sensors.
We present a method of calibrating nonlinear Shack-Hartmann wavefront sensors to enable open-loop wavefront
sensing of atmospheric turbulence. Involving a two-dimensional raster scan of a point source behind a telescope's
primary, this method is robust to aliasing, non-common path errors, linearity error, and truncation error. We have
implemented this technique on the UCO/Lick Laboratory for Adaptive Optics Multi-Conjugate AO (MCAO)
and Multi-Object AO (MOAO) testbed. This testbed has 5 laser guide stars with star-oriented Shack-Hartmann
wavefront sensors that have 4x4 pixel subapertures. We show that the disagreement between these multiple
wavefront sensors on a simulated 10 meter telescope is decreased from 0.80 radians to 0.30 radians RMS for
a full atmosphere (0.6" seeing) with our linearity calibration. This linearity calibration enables simulation of
open-loop MOAO with good Strehl (36% with a simulated science wavelength of 950 nm on-axis) on a 10 meter
aperture. We present a complete error budget for this case, with all budget terms empirically verified through
interferometric methods. We verify that the tomographic error (due to blind modes) as empirically measured on
the testbed is consistent with that predicted by tomographic reconstructions of simulated atmospheres.
Pyramid wavefront sensors offer an alternative to traditional Hartmann sensing for wavefront measurement in astronomical
adaptive optics systems. The Pyramid sensor has been described as a slope sensor with potential sensitivity
gains over the Shack Hartmann sensor, but in actuality seems to exhibit traits of both a slope sensor and a direct phase
sensor. The original configuration, utilizing glass pyramids and modulation techniques, is difficult to implement. We
present results of laboratory experiments using a Pyramid sensor that utilizes a micro-optic lenslet array in place of a
glass pyramid, and does not require modulation. A group of four lenslets forms both the pyramid knife-edge and the
pupil reimaging functions. The lenslet array is fabricated using a technique that pays careful attention to the quality of
the edges and corners of the lenslets. The devices we have tested show less than 1 micron edge and corner imperfections,
making them some of the sharpest edges available. We finish by comparing our results to theoretical wave optic
predictions which clearly show the dual nature of the sensor.
We present first results from the Multi-Conjugate and Multi-Object Adaptive Optics (MCAO and MOAO) testbed, at the UCO/Lick Laboratory for Adaptive Optics (LAO) facility at U.C. Santa Cruz. This testbed is constructed to simulate a 30-m telescope executing MCAO and/or open loop MOAO atmospheric compensation and imaging over 5 arcminutes. It is capable of performing Shack-Hartmann wavefront sensing on up to 8 natural or laser guide stars and 2-3 additional tip/tilt stars. In this paper, we demonstrate improved on-axis correction relative to ground layer adaptive optics (~ 15% Strehl relative to ~ 12%) with a simulated 28-m aperture at a D/r0 corresponding to a science wavelength of 2.6 microns using three laser guide stars on a simulated 41 arcsec radius with a central science object and one deformable mirror at the ground layer.
We describe and evaluate the performance of a wavefront sensor based on curvature sensing which can be used to detect static aberrations given an extended reference source. The description includes a full mathematical treatment of the sensor signal, as well as how this signal is relate to the Laplacian of the wavefront. Evaluation of the technique is performed with computer simulations. A Monte-Carlo simulation is utilized to evaluate the performance of the technique in the presence of noise. The sensor was found to provide accurate measurement of the wavefront coefficients on high-contrast extended objects. It behaves well in the presence of a field stop, and in the presence of additive Gaussian noise.
We present results of simulations involving a curvature-based wavefront sensor which uses an extended pattern as a reference source. The proposed sensor provides measurements of both symmetric and asymmetric aberration terms by comparing the Fourier transforms of two oppositely defocused images. Symmetric terms such as defocus and astigmatism can be measured without regard to the object distribution. The asymmetric terms, such as tip and tilt, rely on averaging the signal over many atmospheric realizations in order to determine the object phase, or on defining an arbitrary reference phase. Only after removal of the object Fourier transform phase can the asymmetric terms be identified. Although this paper reports on preliminary results, we believe the proposed sensor will be useful for both real-time compensation of atmospheric distortions while imaging the Sun, and post-facto compensation of optical misalignments in Earth-pointing satellites.
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