Astronomical adaptive optics (AO) is a critical approach to enable ground-based diffraction-limited imaging and high contrast science, with the potential to enable habitable exoplanet imaging on future extremely large telescopes. However, AO systems must improve significantly to enable habitable exoplanet imaging. Time lag between the end of an exposure and end of deformable mirror commands being applied in an AO loop is now the dominant error term in many extreme AO systems (e.g., Poyneer et al. 2016), and within that lag component detector read time is becoming non-negligible (e.g., Cetre et al. 2018). This term will decrease as faster detector readout capabilities are developed by vendors. In complement, we have developed a modified Shack Hartmann Wavefront Sensor (SHWFS) to address this problem called the Focal-plane Actualized Shifted Technique Realized for a SHWFS (fastrSHWFS). The novelty of this design is to replace the usual lenslet array with a bespoke pupil-plane phase mask that redistributes the spot pattern on the detector into a rectangular array with a custom aspect ratio (in an extreme case, if the detector size can accommodate it, the array can be a single line). We present the fastrSHWFS concept and preliminary laboratory tests. For some detectors and AO systems, the fastrSHWFS technique can decrease the read time per frame compared to a regular SHWFS by up to 30x, supporting the goal of reduced AO lag needed to eventually enable habitable exoplanet imaging.
Focal plane wavefront sensing techniques are generally limited to using imaging systems that have below 1% spectral bandwidths, due to the radial “smearing” of speckles from chromatic diffraction that causes optical image magnification over larger spectral bandwidths. Wynne (1979) designed a pair of triplet lenses to optically minimize this chromatic magnification and increase the spectral bandwidth. Such a Wynne corrector could enable focal plane wavefront sensing at up to 50% spectral bandwidths and as a result open enable > 50x higher-speed focal plane wavefront sensing. We present results of the design and laboratory testing of a Wynne corrector prototype, including a detailed tolerancing analysis considering manufactural wavelength ranges and alignment tolerances. These tests show promising results that this technology can be deployed to current and future high speed focal plane wavefront sensing instruments to enable significant performance enhancements. This document number is LLNL-ABS-857246.
The LSST Camera is a complex, highly integrated instrument for the Vera C. Rubin Observatory. Now that the assembly is complete, we present the highlights of the LSST Camera assembly: successful installation of all Raft Tower Modules (RTM) into the cryostat, integration of the world’s largest lens with the camera body, and successful integration and testing of the shutter and filter exchange systems. While the integration of the LSST Camera is a story of success, there were challenges faced along the way which we present: component failures, late design changes, and facility infrastructure issues.
The performance of high-contrast AO instruments (GPI, SPHERE, ScEXAO, MagAO) and other systems that operate at visible wavelengths can be severely hampered by control system latencies and temporal wavefront errors. In high-contrast systems, temporal errors and delays are manifest as high spatial frequency wavefront residuals that scatter light into the controllable region of the PSF and diminish contrast, an effect that is particularly severe when atmospheric coherence times are short. Solutions that have been proposed include lower latency electronics, deformable mirrors with lower mechanical response times, and specialized control algorithms such as predictive control. These advancements will be necessary for achieving the latency goals of high actuator count systems on future Extremely Large Telescopes (ELTs), including NFIRAOS+ and PFI on the Thirty Meter Telescope, upgrading the performance of existing highcontrast systems, and pushing adaptive optics to visible wavelengths. LLAMAS (Low-Latency Adaptive Optical Mirror System) is a fully funded adaptive optics system at the Lawrence Livermore National Laboratory site that will test these techniques in an integrated, real time, closed-loop AO system. With a total system latency goal of ~100 microseconds (including mechanical response time, not including frame integration), LLAMAS will achieve an order of magnitude improvement in AO system latencies over the current generation of high-contrast AO systems. The woofer/tweeter architecture will incorporate a 492-actuator Boston Micromachines MEMS device mapping 24 actuators across a circular pupil. The tweeter mirror will be paired with a specialized low-latency driver, delivering less than 40 microseconds electronic and mechanical latency (10 – 90%). The real-time control computer will utilize the computationally efficient Fourier Transform Reconstructor with a predictive Kalman filter with a goal of completing all computations and reconstructing the wavefront in less than 20 microseconds. LLAMAS will be fully integrated with a 21×21 lenslet Shack-Hartmann sensor by January 2019. These proceedings describe the LLAMAS design, characterize the performance of its low-latency componentry, and discuss the relevance of the design for future high-contrast, visiblelight, and high actuator count AO systems on ELTs.
The Integration and Verification Testing of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 giga-pixel focal plane mosaic of 189 CCDs with in-vacuum controllers and readout, dedicated guider and wavefront CCDs, a three element corrector with a 1.6-meter diameter initial optic, six optical filters covering wavelengths from 320 to 1000 nm with a novel filter exchange mechanism, and camera-control and data acquisition capable of digitizing each image in two seconds. In this paper, we describe the integration processes under way to assemble the Camera and the associated verification testing program. The Camera assembly proceeds along two parallel paths: one for the focal plane and cryostat and the other for the Camera structure itself. A range of verification tests will be performed interspersed with assembly to verify design requirements with a test-as-you-build methodology. Ultimately, the cryostat will be installed into the Camera structure as the two assembly paths merge, and a suite of final Camera system tests performed. The LSST Camera is scheduled for completion and delivery to the LSST observatory in 2020.
The Gemini Planet Imager (GPI) is a facility extreme-AO high-contrast instrument – optimized solely for study of faint companions – on the Gemini telescope. It combines a high-order MEMS AO system (1493 active actuators), an apodized pupil Lyot coronagraph, a high-accuracy IR post-coronagraph wavefront sensor, and a near-infrared integral field spectrograph. GPI incorporates several other novel features such as ultra-high quality optics, a spatially-filtered wavefront sensor, and new calibration techniques. GPI had first light in November 2013. This paper presnets results of first-light and performance verification and optimization and shows early science results including extrasolar planet spectra and polarimetric detection of the HR4696A disk. GPI is now achieving contrasts approaching 10-6 at 0.5” in 30 minute exposures.
We present an overview of the design of IRIS, an infrared (0.84 - 2.4 micron) integral field spectrograph and imaging
camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront
sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system
(NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of
4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high
redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes
the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral
field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a
very large vacuum cryogenic system.
The Gemini Planet Imager instrument's adaptive optics (AO) subsystem was designed specifically to facilitate high-contrast imaging. It features several new technologies, including computationally efficient wavefront reconstruction with the Fourier transform, modal gain optimization every 8 seconds, and the spatially filtered wavefront sensor. It also uses a Linear-Quadratic-Gaussian (LQG) controller (aka Kalman filter) for both pointing and focus. We present on-sky performance results from verification and commissioning runs from December 2013 through May 2014. The efficient reconstruction and modal gain optimization are working as designed. The LQG controllers effectively notch out vibrations. The spatial filter can remove aliases, but we typically use it oversized by about 60% due to stability problems.
The Gemini Planet Imager (GPI) is a complex optical system designed to directly detect the self-emission of young
planets within two arcseconds of their host stars. After suppressing the starlight with an advanced AO system and
apodized coronagraph, the dominant residual contamination in the focal plane are speckles from the atmosphere and
optical surfaces. Since speckles are diffractive in nature their positions in the field are strongly wavelength dependent,
while an actual companion planet will remain at fixed separation. By comparing multiple images at different
wavelengths taken simultaneously, we can freeze the speckle pattern and extract the planet light adding an order of
magnitude of contrast. To achieve a bandpass of 20%, sufficient to perform speckle suppression, and to observe the
entire two arcsecond field of view at diffraction limited sampling, we designed and built an integral field spectrograph
with extremely low wavefront error and almost no chromatic aberration. The spectrograph is fully cryogenic and
operates in the wavelength range 1 to 2.4 microns with five selectable filters. A prism is used to produce a spectral
resolution of 45 in the primary detection band and maintain high throughput. Based on the OSIRIS spectrograph at
Keck, we selected to use a lenslet-based spectrograph to achieve an rms wavefront error of approximately 25 nm. Over
36,000 spectra are taken simultaneously and reassembled into image cubes that have roughly 192x192 spatial elements
and contain between 11 and 20 spectral channels. The primary dispersion prism can be replaced with a Wollaston prism
for dual polarization measurements. The spectrograph also has a pupil-viewing mode for alignment and calibration.
The Hartmann Sensor is a simple and well-established method to interrogate wavefront quality. Recently the Hartmann sensor has been used at very short wavelengths, including the extreme UV. Here we consider the Hartmann sensor and its ability to measure the wavefront of an x-ray beam. We use both analytic methods and a wave-optics, Fresnel-diffraction simulation. The Hartmann sensor samples the wavefront, which means that it is susceptible to aliasing (the non-linear phenomenon where high-spatial frequency components are incorrectly measured as low-spatial frequency components). Our analysis shows that aliasing is more severe in the Hartmann sensor than in the corresponding (optical) Shack-Hartmann. Aliasing worsens as Hartmann hole size shrinks. The wave-optics simulations show that for reasonable optics-polishing errors and Hartmann mask design, aliasing errors can be of the same magnitude as the phase that is to be measured.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, telescope design feeding a camera system that
includes a set of broad-band filters and three refractive corrector lenses to produce a flat field at the focal plane with a
wide field of view. Optical design of the camera lenses and filters is integrated in with the optical design of telescope
mirrors to optimize performance. We discuss the rationale for the LSST camera optics design, describe the methodology
for fabricating, coating, mounting and testing the lenses and filters, and present the results of detailed analyses
demonstrating that the camera optics will meet their performance goals.
The Gemini Planet Imager is a next-generation instrument for the direct detection and characterization of young warm exoplanets, designed to be an order of magnitude more sensitive than existing facilities. It combines a 1700-actuator adaptive optics system, an apodized-pupil Lyot coronagraph, a precision interferometric infrared wavefront sensor, and a integral field spectrograph. All hardware and software subsystems are now complete and undergoing integration and test at UC Santa Cruz. We will present test results on each subsystem and the results of end-to-end testing. In laboratory testing, GPI has achieved a raw contrast (without post-processing) of 10-6 5σ at 0.4”, and with multiwavelength speckle suppression, 2x10-7 at the same separation.
We present performance results, from in-lab testing, of the Integral Field Spectrograph (IFS) for the Gemini Planet Imager (GPI). GPI is a facility class instrument for the Gemini Observatory with the primary goal of directly detecting young Jovian planets. The GPI IFS is based on concepts from the OSIRIS instrument at Keck and utilizes an infrared transmissive lenslet array to sample a rectangular 2.8 x 2.8 arcsecond field of view. The IFS provides low-resolution spectra across five bands between 1 and 2.5μm. Alternatively, the dispersing element can be replaced with a Wollaston prism to provide broadband polarimetry across the same five filter bands. The IFS construction was based at the University of California, Los Angeles in collaboration with the Université de Montr eal, Immervision and Lawrence Livermore National Laboratory. During its construction, we encountered an unusual noise source from microphonic pickup by the Hawaii-2RG detector. We describe this noise and how we eliminated it through vibration isolation. The IFS has passed its preship review and was shipped to University of California, Santa Cruz at the end of 2011 for integration with the remaining sub-systems of GPI. The IFS has been integrated with the rest of GPI and is delivering high quality spectral datacubes of GPI's coronagraphic field.
The Gemini Planet Imager (GPI) is a facility instrument under construction for the 8-m Gemini South telescope. This
paper describes the methods used for optical alignment of the adaptive optics (AO) bench. The optical alignment of the
off-axis paraboloid mirrors was done using a pre-alignment method utilizing a HeNe laser and alignment telescopes
followed by a fine-tuning using a Shack-Hartmann wavefront sensor and a shear plate. A FARO arm measuring system
was used to place the fiducials for the alignment. Using these methods the AO bench was aligned to 13nm RMS of
wavefront error.
KEYWORDS: Satellites, Space telescopes, Sensors, Stars, Telescopes, Signal to noise ratio, Detection and tracking algorithms, Satellite imaging, Imaging systems, Global Positioning System
The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nanosatellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed and deployed to demonstrate the main elements of the STARE concept. We first give an overview of the STARE program. The details of the optical imaging payload for the STARE pathfinder CubeSats are then described, followed by a description of the track detection algorithm that will be used on the images it acquires. Finally, simulation results that highlight the effectiveness of the mission are presented.
Exoplanet imaging is driving a race to higher contrast imaging, both from earth and from space. Next-generation
instruments such as the Gemini Planet Imager (GPI) and SPHERE are designed to achieve contrast ratios of
10-6 - 10-7 this requires very good wavefront correction and coronagraphic control of diffraction. GPI is a
facility instrument, now in integration and test, with first light on the 8-m Gemini South telescope expected
by the middle of 2012. It combines a 1700 subaperture AO system using a MEMS deformable mirror, an
apodized-pupil Lyot coronagraph, a high-accuracy IR interferometric wavefront calibration system, and a nearinfrared
integral field spectrograph to allow detection and characterization of self-luminous extrasolar planets
at planet/star contrast ratios of 10-7. In this paper we will discuss the status of the integration and test now
taking place at the University of Santa Cruz California.
KEYWORDS: Satellites, Sensors, Stars, Space telescopes, Signal to noise ratio, Image segmentation, Detection and tracking algorithms, Satellite imaging, Telescopes, Space operations
The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information
needed to help satellite operators avoid collisions in space by using a network of nano-satellites to determine
more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program,
two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed
and deployed to demonstrate the main elements of the STARE concept. In this paper, we first give an overview
of the STARE program. We then describe the details of the optical imaging payload for the STARE pathfinder
CubeSats, including the optical design and the sensor characterization. Finally, we discuss the track detection
algorithm that will be used on the images acquired by the payload.
We briefly review the development history of the Gemini Planet Imager's 4K Boston Micromachines MEMS
deformable mirror. We discuss essential calibration steps and algorithms to control the MEMS with nanometer
precision, including voltage-phase calibration and influence function characterization. We discuss the integration
of the MEMS into GPI's Adaptive Optics system at Lawrence Livermore and present experimental results of 1.5
kHz closed-loop control. We detail mitigation strategies in the coronagraph to reduce the impact of abnormal
actuators on final image contrast.
Forbes introduced the usage of Gaussian quadratures in optical design for circular pupils and fields, and for a specific
visible wavelength band. In this paper, Gaussian quadrature methods of selecting rays in ray-tracing are derived for noncircular
pupil shapes, such as obscured and vignetted apertures. In addition, these methods are generalized for square
fields, and for integrating performance over arbitrary wavelength bands. Integration over wavelength is aided by the use
of a novel chromatic coordinate. These quadratures achieve low calculations with fewer rays (by orders of magnitude)
than uniform sampling schemes.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design,
with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3
lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square
degree field and ultraviolet to near infrared wavelengths.
We describe the image quality error budget analysis methodology which includes effects from optical and
optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature
gradients, gravity, pressure, stress, birefringence, and vibration.
The Gemini Planet Imager (GPI) is an extreme AO coronagraphic integral field unit YJHK spectrograph destined
for first light on the 8m Gemini South telescope in 2011. GPI fields a 1500 channel AO system feeding an
apodized pupil Lyot coronagraph, and a nIR non-common-path slow wavefront sensor. It targets detection and
characterizion of relatively young (<2GYr), self luminous planets up to 10 million times as faint as their primary
star. We present the coronagraph subsystem's in-lab performance, and describe the studies required to specify
and fabricate the coronagraph. Coronagraphic pupil apodization is implemented with metallic half-tone screens
on glass, and the focal plane occulters are deep reactive ion etched holes in optically polished silicon mirrors. Our
JH testbed achieves H-band contrast below a million at separations above 5 resolution elements, without using
an AO system. We present an overview of the coronagraphic masks and our testbed coronagraphic data. We
also demonstrate the performance of an astrometric and photometric grid that enables coronagraphic astrometry
relative to the primary star in every exposure, a proven technique that has yielded on-sky precision of the order
of a milliarsecond.
We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging
Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by
uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with
certain glass combinations. The design decisions are discussed and the performance of the design ADC is described.
Alternative options and their performance tradeoffs are also presented.
The Infra-Red Imaging Spectrograph (IRIS) is one of the three first light instruments for the Thirty Meter Telescope
(TMT) and is the only one to directly sample the diffraction limit. The instrument consists of a parallel imager and offaxis
Integral Field Spectrograph (IFS) for optimum use of the near infrared (0.84um-2.4um) Adaptive Optics corrected
focal surface. We present an overview of the IRIS spectrograph that is designed to probe a range of scientific targets
from the dynamics and morphology of high-z galaxies to studying the atmospheres and surfaces of solar system objects,
the latter requiring a narrow field and high Strehl performance. The IRIS spectrograph is a hybrid system consisting of
two state of the art IFS technologies providing four plate scales (4mas, 9mas, 25mas, 50mas spaxel sizes). We present
the design of the unique hybrid system that combines the power of a lenslet spectrograph and image slicer spectrograph
in a configuration where major hardware is shared. The result is a powerful yet economical solution to what would
otherwise require two separate 30m-class instruments.
We present an overview of the design of IRIS, an infrared (0.85 - 2.5 micron) integral field spectrograph and imaging
camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront
sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system
(NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of
4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high
redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes
the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral
field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a
very large vacuum cryogenic system.
The Gemini Planet Imager (GPI) is a new facility instrument to be commissioned at the 8-m Gemini South
telescope in early 2011. It combines of several subsystems including a 1500 subaperture Extreme Adaptive
Optics system, an Apodized Pupil Lyot Coronagraph, a near-infrared high-accuracy interferometric wavefront
sensor, and an Integral Field Unit Spectrograph, which serves as the science instrument. GPI's main scientific
goal is to detect and characterize relatively young (<2GYr), self luminous planets with planet-star brightness
ratios of ≤ 10-7 in the near infrared. Here we present an overview of the coronagraph subsystem, which includes
a pupil apodization, a hard-edged focal plane mask and a Lyot stop. We discuss designs optimization, masks
fabrication and testing. We describe a near infrared testbed, which achieved broadband contrast (H-band)
below 10-6 at separations > 5λ/D, without active wavefront control (no deformable mirror). We use Fresnel
propagation modeling to analyze the testbed results.
Visible Light Laser Guidestar Experiments (ViLLaGEs) is a new Micro-Electro Mechanical Systems (MEMS)
based visible-wavelength adaptive optics (AO) testbed on the Nickel 1-meter telescope at Lick Observatory. Closed
loop Natural Guide Star (NGS) experiments were successfully carried out during engineering during the fall of
2007. This is a major evolutionary step, signaling the movement of AO technologies into visible light with a MEMS
mirror. With on-sky Strehls in I-band of greater than 20% during second light tests, the science possibilities have
become evident.
Described here is the advanced engineering used in the design and construction of the ViLLaGEs system, comparing
it to the LickAO infrared system, and a discussion of Nickel dome infrastructural improvements necessary for this
system. A significant portion of the engineering discussion revolves around the sizable effort that went towards
eliminating flexure. Then, we detail upgrades to ViLLaGEs to make it a facility class instrument. These upgrades
will focus on Nyquist sampling the diffraction limited point spread function during open loop operations,
motorization and automation for technician level alignments, adding dithering capabilities and changes for near
infrared science.
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.
The Gemini Planet Imager (GPI) is a future high-order coronagraphic adaptive optics system optimized for the search
and analysis of Jupiter-like exoplanets around nearby young 10-1000Myr stars. In this paper, an on-axis Fresnel
wavefront propagation model of GPI is presented. The main goal of this work is to confirm that the current GPI design
will reach its 10-7 contrast requirement. The model, assembled using the PROPER IDL library, is used to properly
simulate out-of-pupil-plane and finite size optics. A spectral data cube at GPI spectral resolution R=45 in H-band is
obtained to estimate the GPI contrast as a function of wavelength. This cube is then used to evaluate the speckle
suppression performance of the Simultaneous Spectral Differential Imaging (SSDI) technique. It is shown that GPI
should achieve a photon noise limited 10-7 contrast when using a simple SSDI post-processing on an H=5 star and a 1h
observing sequence. Finally, a long exposure data cube is obtained by combining the speckle contributions of an average
atmosphere and GPI optics. That final long-exposure contrast as a function of wavelength can be used to estimate the
GPI exoplanet characterization accuracy, and to evaluate, using Monte-Carlo simulations, the expected exoplanet survey
performance.
Laser guide star wavefront sensors (WFS) using pulsed lasers can benefit from dynamic refocusing techniques which
synchronously adjust the focus of the wavefront as the light returns from the scattering layer so as to maintain a constant
axial image location. Existing techniques involve pulsating discrete mirrors and high-speed segmented MEMS in the
WFS path. A different approach is presented here, which uses a pair of rotating phase plates with cylindrical or Alvarezlens-
style tracks near the WFS pupil. Rotational speeds and disk sizes similar to that used for compact disc operation are
proposed. The plates can be manufactured by numerical machining of transparent plastic materials or as diffractive
components.
The Gemini Planet Imager (GPI) is a facility instrument under construction for the 8-m Gemini South telescope. It
combines a 1500 subaperture AO system using a MEMS deformable mirror, an apodized-pupil Lyot coronagraph, a
high-accuracy IR interferometer calibration system, and a near-infrared integral field spectrograph to allow detection and
characterization of self-luminous extrasolar planets at planet/star contrast ratios of 10-7. I will discuss the evolution from
science requirements through modeling to the final detailed design, provide an overview of the subsystems and show
models of the instrument's predicted performance.
The Lick Observatory is pursuing new technologies for adaptive optics that will enable feasible low cost laser guidestar
systems for visible wavelength astronomy. The Villages system, commissioned at the 40 inch Nickel Telescope this past
Fall, serves as an on-sky testbed for new deformable mirror technology (high-actuator count MEMS devices), open-loop
wavefront sensing and control, pyramid wavefront sensing, and laser uplink correction. We describe the goals of our
experiments and present the early on-sky results of AO closed-loop and open-loop operation. We will also report on our
plans for on-sky tests of the direct-phase measuring pyramid-lenslet wavefront sensor and plans for installing a laser
guidestar system.
Several high-contrast imaging systems are currently under construction to enable the detection of extra-solar planets. In
order for these systems to achieve their objectives, however, there is considerable developmental work and testing which
must take place. Given the need to perform these tests, a spatially-filtered Shack-Hartmann adaptive optics system has
been assembled to evaluate new algorithms and hardware configurations which will be implemented in these future
high-contrast imaging systems. In this article, construction and phase measurements of a membrane "woofer" mirror are
presented. In addition, results from closed-loop operation of the assembled testbed with static phase plates are presented.
The testbed is currently being upgraded to enable operation at speeds approaching 500 hz and to enable studies of the
interactions between the woofer and tweeter deformable mirrors.
The MEMS-AO/Villages project consists of a series of on-sky experiments that will demonstrate key new
technologies for the next generation of adaptive optics systems for large telescopes. One of our first goals is to
demonstrate the use of a micro-electro-mechanical systems (MEMS) deformable mirror as the wavefront correcting
element. The system is mounted the 1-meter Nickel Telescope at the UCO/Lick Observatory on Mount Hamilton. It
uses a 140 element (10 subapertures across) MEMS deformable mirror and is designed to produce diffraction-limited
images at wavelengths from 0.5 to 1.0 microns. The system had first light on the telescope in October 2007.
Here we report on the results of initial on-sky tests.
We present a summary of our current results from the Extreme Adaptive Optics (ExAO) Testbed and the design
and status of its coronagraphic upgrade. The ExAO Testbed at the Laboratory for Adaptive Optics at UCO/Lick
Observatory is optimized for ultra-high contrast applications requiring high-order wavefront control. It is being
used to investigate and develop technologies for the Gemini Planet Imager (GPI). The testbed is equipped with
a phase shifting diffraction interferometer (PSDI), which measures the wavefront with sub-nm precision and
accuracy. The testbed also includes a 1024-actuator Micro Electro Mechanical Systems (MEMS) deformable
mirror manufactured by Boston Micromachines. We present a summary of the current results with the testbed
encompassing MEMS flattening via PSDI, MEMS flattening via a Shack-Hartmann wavefront sensor (with and
without spatial filtering), the introduction of Kolmogorov phase screens, and contrast in the far-field. Upgrades
in progress include adding additional focal and pupil planes to better control scattered light and allow alternative
coronagraph architectures, the introduction and testing of high-quality reflecting optics, and a variety of input
phase aberrations. Ultimately, the system will serve as a full prototype for GPI.
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.
The Thirty Meter Telescope (TMT), the next generation giant segmented mirror telescope, will have unprecedented
astronomical science capability. Since science productivity is greatly enhanced through the use of adaptive optics, the
TMT science team has decided that adaptive optics should be implanted on all the IR instruments. We present the
results of a feasibility study for the adaptive optics systems on the infrared multi-object spectrograph, IRMOS and
report on the design concepts and architectural options. The IRMOS instrument is intended to produce integral field
spectra of up to 20 objects distributed over a 5 arcminute field of regard. The IRMOS adaptive optics design is unique
in that it will use multiple laser guidestars to reconstruct the atmospheric volume tomographically, then apply AO
correction for each science direction independently. Such a scheme is made technically feasible and cost effective
through the use of micro-electromechanical system (MEMS) deformable mirrors.
Direct detection of extrasolar Jovian planets is a major scientific motivation for the construction of future extremely
large telescopes such as the Thirty Meter Telescope (TMT). Such detection will require dedicated high-contrast AO
systems. Since the properties of Jovian planets and their parent stars vary enormously between different populations, the
instrument must be designed to meet specific scientific needs rather than a simple metric such as maximum Strehl ratio.
We present a design for such an instrument, the Planet Formation Imager (PFI) for TMT. It has four key science
missions. The first is the study of newly-formed planets on 5-10 AU scales in regions such as Taurus and Ophiucus -
this requires very small inner working distances that are only possible with a 30m or larger telescope. The second is a
robust census of extrasolar giant planets orbiting mature nearby stars. The third is detailed spectral characterization of
the brightest extrasolar planets. The final targets are circumstellar dust disks, including Zodiacal light analogs in the
inner parts of other solar systems. To achieve these, PFI combines advanced wavefront sensors, high-order MEMS
deformable mirrors, a coronagraph optimized for a finely- segmented primary mirror, and an integral field spectrograph.
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.
Direct observation of extrasolar Jovian planets will enable detailed investigation and understanding of the formation of these planet populations and also of their relative abundance. Future large telescopes, such as the Thirty Meter Telescope(TMT), will enable the study of such planet populations at relatively small working distances from the parent star. We present an analysis of an extreme adaptive optics system utilizing a self-referencing phase-shifting interferometer as the primary wave-front sensor. A module of the adaptive optics system consists of a conventional Shack-Hartmann wave-front sensor to provide the initial start-up of the adaptive optics system, thereby placing a significant amount of energy into the core of the point spread function which will act as the reference for the primary interferometric wave-front sensor. The interferometric-based wave-front sensor is shown to provide a significant improvement in the achievable contrast ratio compared with conventional adaptive optics systems containing Shack-Hartmann wave-front sensors.
Adaptive optics systems typically include an optical relay that simultaneously images the science field to be corrected and also a set of pupil planes conjugate to the deformable mirror of the system. Often, in the optical spaces where DM's are placed, the pupils are aberrated, leading to a displacement and/or distortion of the pupil that varies according to field position--producing a type of anisoplanatism, i.e., a degradation of the AO correction with field angle. The pupil aberration phenomenon is described and expressed in terms of Seidel aberrations. An expression for anisoplanatism as a function of pupil distortion is derived, an example of an off-axis parabola is given, and a convenient method for controlling pupil-aberration-generated anisoplanatism is proposed.
We describe an exploratory optical design for the Narrow Field InfraRed Adaptive Optics (AO) System (NFIRAOS) Petite, a proposed adaptive optics system for the Thirty Meter Telescope Project. NFIRAOS will feed infrared spectrograph and wide-field imaging instruments with a diffraction limited beam. The adaptive optics system will require multi-guidestar tomographic wavefront sensing (WFS) and multi-conjugate AO correction. The NFIRAOS Petite design specifications include two small 60 mm diameter deformable mirrors (DM's) used in a woofer/tweeter or multiconjugate arrangement. At least one DM would be a micro-electromechanical system (MEMS) DM. The AO system would correct a 10 to 30 arcsec diameter science field as well as laser guide stars (LGS's) located within a 60 arcsec diameter field and low-order or tip/tilt natural guide stars (NGS's) within a 60 arcsec diameter field. The WFS's are located downstream of the DM's so that they can be operated in true closed-loop, which is not necessarily a given in extremely large telescope adaptive optics design. The WFS's include adjustable corrector elements which correct the static aberrations of the AO relay due to field position and LGS distance height.
Correlation wave-front sensing can improve Adaptive Optics (AO) system performance in two keys areas. For point-source-based AO systems, Correlation is more accurate, more robust to changing conditions and provides lower noise than a centroiding algorithm. Experimental results from the Lick AO system and the SSHCL laser AO system confirm this. For remote imaging, Correlation enables the use of extended objects for wave-front sensing. Results from short horizontal-path experiments will show algorithm properties and requirements.
As adaptive optics (AO) matures, it becomes possible to envision AO systems oriented towards specific important scientific goals rather than general-purpose systems. One such goal for the next decade is the direct imaging detection of extrasolar planets. An "extreme" adaptive optics (ExAO) system optimized for extrasolar planet detection will have very high actuator counts and rapid update rates - designed for observations of bright stars - and will require exquisite internal calibration at the nanometer level. In addition to extrasolar planet detection, such a system will be capable of characterizing dust disks around young or mature stars, outflows from evolved stars, and high Strehl ratio imaging even at visible wavelengths. The NSF Center for Adaptive Optics has carried out a detailed conceptual design study for such an instrument, dubbed the eXtreme Adaptive Optics Planet Imager or XAOPI. XAOPI is a 4096-actuator AO system, notionally for the Keck telescope, capable of achieving contrast ratios >107 at angular separations of 0.2-1". ExAO system performance analysis is quite different than conventional AO systems - the spatial and temporal frequency content of wavefront error sources is as critical as their magnitude. We present here an overview of the XAOPI project, and an error budget highlighting the key areas determining achievable contrast. The most challenging requirement is for residual static errors to be less than 2 nm over the controlled range of spatial frequencies. If this can be achieved, direct imaging of extrasolar planets will be feasible within this decade.
Adaptive optics (AO), a mature technology developed for astronomy to compensate for the effects of atmospheric turbulence, can also be used to correct the aberrations of the eye. The classic phoropter is used by ophthalmologists and optometrists to estimate and correct the lower-order aberrations of the eye, defocus and astigmatism, in order to derive a vision correction prescription for their patients. An adaptive optics phoropter measures and corrects the aberrations in the human eye using adaptive optics techniques, which are capable of dealing with both the standard low-order aberrations and higher-order aberrations, including coma and spherical aberration. High-order aberrations have been shown to degrade visual performance for clinical subjects in initial
investigations. An adaptive optics phoropter has been designed and constructed based on a Shack-Hartmann sensor to measure the aberrations of the eye, and a liquid crystal spatial light modulator to compensate for them. This system should produce near diffraction-limited optical image quality at the retina, which will enable investigation of the psychophysical limits of human vision. This paper describes the characterization and operation of the AO phoropter with results from human subject testing.
Astronomical applications of adaptive optics at Lawrence Livermore National Laboratory (LLNL) has a history that extends from 1984. The program started with the Lick Observatory Adaptive Optics system and has progressed through the years to lever-larger telescopes: Keck, and now the proposed CELT (California Extremely Large Telescope) 30m telescope. LLNL AO continues to be at the forefront of AO development and science.
The Lick Observatory laser guide star adaptive optics system has undergone continual improvement and testing as it is being integrated as a facility science instrument on the Shane 3 meter telescope. Both Natural Guide Star (NGS) and Laser Guide Star (LGS) modes are now used in science observing programs. We report on system performance results as derived from data taken on both science and engineering nights and also describe the newly developed on-line techniques for seeing and system performance characterization. We also describe the future enhancements to the Lick system that will enable additional science goals such as long-exposure spectroscopy.
The California Extremely Large Telescope (CELT) project has recently completed a 12-month conceptual design phase that has investigated major technology challenges in a number of Observatory subsystems, including adaptive optics (AO). The goal of this effort was not to adopt one or more specific AO architectures. Rather, it was to investigate the feasibility of adaptive optics correction of a 30-meter diameter telescope and to suggest realistic cost ceilings for various adaptive optics capabilities. We present here the key design issues uncovered during conceptual design and present two non-exclusive "baseline" adaptive optics concepts that are expected to be further developed during the following preliminary design phase. Further analysis, detailed engineering trade studies, and certain laboratory and telescope experiments must be performed, and key component technology prototypes demonstrated, prior to adopting one or more adaptive optics systems architectures for realization.
The multi-conjugate adaptive optics (MCAO) system design for the Gemini-South 8-meter telescope will provide near-diffraction-limited, highly uniform atmospheric turbulence compensation at near-infrared wavelengths over a 2 arc minute diameter field-of-view. The design includes three deformable mirrors optically conjugate to ranges of 0, 4.5, and 9.0 kilometers with 349, 468, and 208 actuators, five 10-Watt-class sodium laser guide stars (LGSs) projected from a laser launch telescope located behind the Gemini secondary mirror, five Shack-Hartmann LGS wavefront sensors of order 16 by 16, and three tip/tilt natural guide star (NGS) wavefront sensors to measure tip/tilt and tilt anisoplanatism wavefront errors. The WFS sampling rate is 800 Hz. This paper provides a brief overview of sample science applications and performance estimates for the Gemini South MCAO system, together with a summary of the performance requirements and/or design status of the principal subsystems. These include the adaptive optics module (AOM), the laser system (LS), the beam transfer optics (BTO) and laser launch telescope (LLT), the real time control (RTC) system, and the aircraft safety system (SALSA).
The Lick Observatory laser guide star adaptive optics system has been significantly upgraded over the past two years in order to establish it as a facility science instrument on the Shane 3 meter telescope. Natural Guide Star (NGS) mode has been in use in regular science observing programs for over a year. The Laser Guide Star (LGS) mode has been tested in engineering runs and is now starting to do science observing. In good seeing conditions, the system produces K-band Strehl ratios >0.7 (NGS) and >0.6 (LGS). In LGS mode tip/tilt guiding is achieved with a V~16 natural star anywhere inside a 1 arcminute radius field, which provides about 50% sky coverage. This enables diffraction-limited imaging of regions where few bright guidestars suitable for NGS mode are available. NGS mode requires at least a V~13 guidestar and has a sky coverage of <1%. LGS science programs will include high resolution studies of galaxies, active galactic nuclei, QSO host galaxies and dim pre-main sequence stars.
In 1999, we presented our plan to upgrade the adaptive optics (AO) system on the Lick Observatory Shane telescope (3m) from a prototype instrument pressed into field service to a facility instrument. This paper updates the progress of that plan and details several important improvements in the alignment and calibration of the AO bench. The paper also includes a discussion of the problems seen in the original design of the tip/tilt (t/t) sensor used in laser guide star mode, and how these problems were corrected with excellent results.
We discuss the design and implementation of a low-cost, high-resolution adaptive optics test-bed for vision research. It is well known that high-order aberrations in the human eye reduce optical resolution and limit visual acuity. However, the effects of aberration-free eyesight on vision are only now beginning to be studied using adaptive optics to sense and correct the aberrations in the eye. We are developing a high-resolution adaptive optics system for this purpose using a Hamamatsu Parallel Aligned Nematic Liquid Crystal Spatial Light Modulator. Phase-wrapping is used to extend the effective stroke of the device, and the wavefront sensing and wavefront correction are done at different wavelengths. Issues associated with these techniques will be discussed.
In the near future, the Gemini Observatory will offer Laser Guide Star Adaptive Optics (LGS AO) observations on both Gemini North and South telescopes. The Gemini North AO system will use a 10W-class sodium laser to produce one laser guide star at Mauna Kea, Hawaii, whereas the Gemini South AO System will use up to five such lasers or a single 50W-class laser to produce one to five sodium beacons at Cerro Pachon, Chile. In this paper we discuss the similarities and differences between the Gemini North and South Laser Guide Star Systems. We give a brief overview of the Gemini facility Adaptive Optics systems and the on-going laser research and development program to procure efficient, affordable and reliable lasers. The main part of the paper presents the top-level requirements and preliminary designs for four of the Gemini North and South Laser Guide Star subsystems: the Laser Systems (LS), Beam Transfer Optics (BTO), Laser Launch Telescopes (LLT), and their associated Periscopes.
While the theory behind design of multiconjugate adaptive optics (MCAO) systems is growing, there is still a paucity of experience building and testing such instruments. We propose using the Lick adaptive optics (AO) system as a basis for demonstrating the feasibility/workability of MCAO systems, testing underlying assumptions, and experimenting with different approaches to solving MCAO system issues.
Direct detection of photons emitted or reflected by an extrasolar planet is an extremely difficult but extremely exciting application of adaptive optics. Typical contrast levels for an extrasolar planet would be 109 - Jupiter is a billion times fainter than the sun. Current adaptive optics systems can only achieve contrast levels of 106, but so-called extreme adaptive optics systems with 104 -105 degrees of freedom could potentially detect extrasolar planets. We explore the scaling laws defining the performance of these systems, first set out by Angel (1994), and derive a different definition of an optimal system. Our sensitivity predictions are somewhat more pessimistic than the original paper, due largely to slow decorrelation timescales for some noise sources, though choosing to site an ExAO system at a location with exceptional r0 (e.g. Mauna Kea) can offset this. We also explore the effects of segment aberrations in a Keck-like telescope on ExAO; although the effects are significant, they can be mitigated through Lyot coronagraphy.
We have developed a high-resolution wavefront control system based on an optically addressed nematic liquid crystal spatial light modulator with several hundred thousand phase control points, a Shack-Hartmann wavefront sensor with two thousand subapertures, and an efficient reconstruction algorithm using Fourier transform techniques. We present quantitative results of experiments to characterize the performance of this system.
California Institute of Technology and University of California have begun conceptual design studies for a new telescope for astronomical research at visible and infrared wavelengths. The California Extremely Large Telescope (CELT) is currently envisioned as a filled-aperture, steerable, segmented telescope of approximately 30 m diameter. The key to satisfying many of the science goals of this observatory is the availability of diffraction-limited wavefront control. We describe potential observing modes of CELT, including a discussion of the several major outstanding AO system architectural design issues to be resolved prior to the initiation of the detailed design of the adaptive optics capability.
KEYWORDS: Adaptive optics, Stars, Cameras, Laser guide stars, Point spread functions, Telescopes, Wavefronts, Infrared cameras, Mirrors, Signal to noise ratio
Progress and results of observations with the Lick Observatory Laser Guide Star Adaptive Optics System are presented. This system is optimized for diffraction-limited imaging in the near infrared, 1 - 2 micron wavelength bands. We describe our development efforts in a number of component areas including, a redesign of the optical bench layout, the commissioning of a new infrared science camera, and improvements to the software and user interface. There is also an ongoing effort to characterize the system performance with both natural and laser guide stars and to fold this data into a refined system model. Such a model can be used to help plan future observations, for example, predicting the point-spread function as a function of seeing and guide star magnitude.
Liquid crystal spatial light modulator technology appropriate for high-resolution wavefront control has recently become commercially available. Some of these devices have several hundred thousand controllable degrees of freedom, more than two orders of magnitude greater than the largest conventional deformable mirror. We will present results of experiments to characterize the optical properties of these devices and to utilize them to correct aberrations in an optical system. We will also present application scenarios for these devices in high-power laser systems.
Results of experiments with the laser guide star adaptive optics system on the 3-meter Shane telescope at Lick Observatory have demonstrated a factor of 4 performance improvement over previous results. Stellar images recorded at a wavelength of 2 micrometers were corrected to over 40 percent of the theoretical diffraction-limited peak intensity. For the previous two years, this sodium-layer laser guide star system has corrected stellar images at this wavelength to approximately 10 percent of the theoretical peak intensity limit. After a campaign to improve the beam quality of the laser system, and to improve calibration accuracy and stability of the adaptive optics system using new techniques for phase retrieval and phase-shifting diffraction interferometry, the system performance has been substantially increased. The next step will be to use the Lick system for astronomical science observations, and to demonstrate this level of performance with the new system being installed on the 10-meter Keck II telescope.
Any adaptive optics system must be calibrated with respect to internal aberrations in order for it to properly correct the starlight before it enters the science camera. Typical internal calibration consists of using a point source stimulus at the input to the AO system and recording the wavefront at the output. Two methods for such calibration have been implemented on the adaptive optics system at Lick Observatory. The first technique, Phase Diversity, consists of taking out of focus images with the science camera and using an iterative algorithm to estimate the system wavefront. A second technique sues a newly installed instrument, the Phase-Shifting Diffraction Interferometer, which has the promise of providing very high accuracy wavefront measurements. During observing campaigns in 1998, both of these methods were used for initial calibrations. In this paper we present results and compare the two methods in regard to accuracy and their practical aspects.
A phase-shifting diffraction interferometer (PSDI) has been integrated into an adaptive optics (AO) system developed by LLNL for use on the three meter Shane telescope at Lick Observatory. The interferometer is an all fiber optic design, which is extremely compact. It is useful for calibrating the control sensors, measuring the aberrations of the entire AO optical train, and measuring the influence functions of the individual actuators on the deformable mirror. The PSDI is particularly well suited for this application because it measures converging, quasi-spherical wavefronts, such as are produced by an AO imaging system. Thus, a PSDI can be used to measure the aberrations of the entire AO system, in-situ and without errors introduced by auxiliary optics. This provides an extremely accurate measurement of the optical properties of the AO system.
The performance of a sodium laser guide star adaptive optics system depends crucially on the characteristics of the laser guide star in the sodium layer. System performance is quite sensitive to sodium layer spot radiance, that is, return per unit steradian on the sky, hence we have been working to improve projected beam quality via improvements to the laser and changes to the launched beam format. The laser amplifier was reconfigured to a 'bounce-beam' geometry, which considerably improves wavefront quality and allows a larger round instead of square launch beam aperture. The smaller beacon makes it easier to block the unwanted Rayleigh light and improves the accuracy of Hartmann sensor wavefront measurements in the AO system. We present measurements of the beam quality and of the resulting sodium beacon and compare to similar measurements from last year.
We present the requirements, design, and resulting new layout for the laser guide star/natural guide star adaptive optics (AO) system on the 3-meter Shane telescope at Lick Observatory. This layout transforms our engineering prototype into a stable, reliable, maintainable end-user- oriented system, suitable for use as a facility instrument. Important new features include convenient calibration using proven phase-shifting diffraction interferometer or phase- diversity techniques; a new scatter rejection in LGS mode and better guide-star selection NGS mode; high-sensitivity, wide-field acquisition camera; and significant improvements in adjustment motorization and optomechanical stability.
As part of a team headed by the McDonnell Douglas Helicopter Company and including the Honeywell Systems and Research Division, we have investigated several advanced real-time viewing systems. The study was predicated upon human factors drivers that lead to specifications for several different types of systems. These include systems with 0.6 mr resolution and 170 degree(s) X 50 degree(s), 100 degree(s) X 50 degree(s), and 50 degree(s) X 50 degree(s) fields of view.
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