The MMT Adaptive optics exoPlanet characterization System (MAPS) is currently in its engineering phase, operating on sky at the MMT Telescope. The MAPS Adaptive Secondary Mirror’s actuators are controlled by a closed loop modified PID control law and an open loop feed forward law, which in combination allows for faster actuator response time. An essential element of achieving the secondary’s performance goals involves the process of PID gain tuning. To start, we briefly discuss the design of the MAPS ASM and its actuators. We then describe the actuator positional control system and control law. Next, we discuss a few of the issues that make ASM tuning difficult. We then outline our initial attempts at tuning the actuator controllers, and discuss the use of actuator positional power spectra for both tuning and determining the health and failure states of individual actuators. We conclude by presenting the results of our latest round of tuning configuration trials, which have been successful at decreasing mirror latency, increasing operational mirror modes and improving image PSF.
The MMT AO exoPlanet characterization System is an upgrade for the 6.5-m MMT observatory to the 20-year-old MMTAO adaptive secondary mirror (ASM) with new electronics, a new AO system with two pyramid wavefront sensors spanning the visible through infrared, and a suite of upgraded science cameras optimized for studying the atmospheres of extrasolar planets. We began on-sky engineering and commissioning in October 2022, and have progressed through first light to calibrations at this time. The AO system is complex with its dual wavefront sensors, and the ASM can only be calibrated on-sky. We will present the current status and results of commissioning the MAPS AO system.
The Compute and Control for Adaptive Optics (CACAO) is a free and open-source real-time library for adaptive optics (AO), initially developed for the operation of the 1200+ mode AO loop of Subaru/SCExAO. The scope has expanded since then, through refactorings, the addition of numerous features (predictive control, machine learning), and a substantial improvement of our understanding and configuration of the underlying real-time Linux distribution. We now witness the adoption of the package at multiple facilities, using a variety of cameras and WFSs: non-linear curvature, Shack-Hartmann, Photonic lanterns, and of course the pyWFS. At Subaru, CACAO is the core of the AO3K RTC, which supports legacy NGS and LGS mode, as well as the new high-order wavefront sensors coupled to an ALPAO 3224 deformable mirror. We present developments in algorithms -- bindings for machine learning algorithms, real-time configuration tools -- and user interface tools added in the past few years. We show performance benchmarks on the SCExAO and AO3K systems. We present our future plans to affirm CACAO as the go-to free, open-source RTC toolkit for real-time pipelines in the academic world.
With the commissioning of the refurbished adaptive secondary mirror (ASM) for the 6.5-meter MMT Observatory under way, special consideration had to be made to properly calibrate the mirror response functions to generate an interaction matrix (IM). The commissioning of the ASM is part of the MMT Adaptive optics exo- Planet characterization System (MAPS) upgrade the observatory’s legacy adaptive optics (AO) system. Unlike most AO systems, MAPS employs a convex ASM which prevents the introduction of a calibration source capable of simultaneously illuminating its ASM and wavefront sensor (WFS). This makes calibration of the AO system a significant hurdle in commissioning. To address this, we have employed a hybrid calibration strategy we call the Efficient Synthesis of Calibrations for Adaptive Optics through Pseudo-synthetic and Empirical methods (ESCAPE). ESCAPE combines the DO-CRIME on-sky calibration method with the SPRINT method for computing pseudo-synthetic calibration matrices. To monitor quasi-static system change, the ESCAPE methodology rapidly and continuously generates pseudo-synthetic calibration matrices using continual empirical feedback in either open or closed-loop. In addition, by measuring the current IM in the background while in close-loop, we are also able to measure the optical gains for pyramid wavefront sensor (PyWFS) systems. In this paper, we will provide the mathematical foundation of the ESCAPE calibration strategy and on-sky results from its application in calibrating the MMT Observatory’s ASM. Additionally, we will showcase the validation of our approach from our AO testbed and share preliminary on-sky results from MMT.
The MMT Adaptive Optics exoPlanet Characterization System (MAPS) is a comprehensive update to the first generation MMT adaptive optics system (MMTAO), designed to produce a facility class suite of instruments whose purpose is to image nearby exoplanets. The system’s adaptive secondary mirror (ASM), although comprised in part of legacy components from the MMTAO ASM, represents a major leap forward in design, structure and function. The subject of this paper is the design, operation, achievements and technical issues of the MAPS adaptive secondary mirror. We discuss laboratory preparation for on-sky engineering runs, the results of those runs and the issues we discovered, what we learned about those issues in a follow up period of laboratory work, and the steps we are taking to mitigate them.
The MMT Adaptive optics exoPlanet characterization System (MAPS) is an exoplanet characterization program that encompasses instrument development, observational science, and education. The instrument we are developing for the 6.5m MMT observatory is multi-faceted, including a refurbished 336-actuator adaptive secondary mirror (ASM); two pyramid wavefront sensors (PyWFS's); a 1-kHz adaptive optics (AO) control loop; a high-resolution and long-wavelength upgrade to the Arizona infraRed Imager and Echelle Spectrograph (ARIES); and a new-AO-optimized upgrade to the MMT-sensitive polarimeter (MMT-Pol). With the completed MAPS instrument, we will execute a 60-night science program to characterize the atmospheric composition and dynamics of ~50-100 planets around other stars. The project is approaching first light, anticipated for Summer/Fall of 2022. With the electrical and optical tests complete and passing the review milestone for the ASM’s development, it is currently being tuned. The PyWFS's are being built and integrated in their respective labs: the visible-light PyWFS at the University of Arizona (UA), and the infrared PyWFS at the University of Toronto (UT). The top-level AO control software is being developed at UA, with an on-sky calibration algorithm being developed at UT. ARIES development continues at UA, and MMT-Pol development is at the University of Minnesota. The science and education programs are in planning and preparation. We will present the design and development of the entire MAPS instrument and project, including an overview of lab results and next steps.
The MMTO Adaptive optics exoPlanet characterization System (MAPS) is an ongoing upgrade to the 6.5-meter MMT Observatory on Mount Hopkins in Arizona. MAPS includes an upgraded adaptive secondary mirror (ASM), upgrades to the ARIES spectrograph, and a new AO system containing both an optical and near-infrared (NIR; 0.9-1.8 μm) pyramid wavefront sensor (PyWFS). The NIR PyWFS will utilize an IR-optimized double pyramid coupled with a SAPHIRA detector: a low-read noise electron Avalanche Photodiode (eAPD) array. This NIR PyWFS will improve MAPS’s sky coverage by an order of magnitude by allowing redder guide stars (e.g. K & M-dwarfs or highly obscured stars in the Galactic plane) to be used. To date, the custom designed cryogenic SAPHIRA camera has been fully characterized and can reach sub-electron read noise at high avalanche gain. In order to test the performance of the camera in a closed-loop environment prior to delivery to the observatory, an AO testbed was designed and constructed. In addition to testing the SAPHIRA’s performance, the testbed will be used to test and further develop the proposed on-sky calibration procedure for MMTO’s ASM. We will report on the anticipated performance improvements from our NIR PyWFS, the SAPHIRA’s closed-loop performance on our testbed, and the status of our ASM calibration procedure.
MagAO-X is an extreme adaptive optics (ExAO) instrument for the Magellan Clay 6.5-meter telescope at Las Campanas Observatory in Chile. Its high spatial and temporal resolution can produce data rates of 1 TB/hr or more, including all AO system telemetry and science images. We describe the tools and architecture we use for commanding, telemetry, and science data transmission and storage. The high data volumes require a distributed approach to data processing, and we have developed a pipeline that can scale from a single laptop to dozens of HPC nodes. The same codebase can then be used for both quick-look functionality at the telescope and for post-processing. We present the software and infrastructure we have developed for ExAO data post-processing, and illustrate their use with recently acquired direct-imaging data.
We present the fifth incarnation of the Mid-Infrared Array Camera (MIRAC-5) instrument which will use a new GeoSnap (3 – 13 microns) detector. Advances in adaptive optics (AO) systems and detectors are enabling ground based mid-infrared systems capable of high spatial resolution and deep contrast. As one of the only 3 – 13 micron cameras used in tandem with AO, MIRAC-5 will be complementary to the James Webb Space Telescope (JWST) and capable of characterizing gas giant exoplanets and imaging forming protoplanets (helping to characterize their circumplanetary disks). We describe key features of the MIRAC-5 GeoSnap detector, a long-wave Mercury-Cadmium-Telluride (MCT) array produced by Teledyne Imaging Sensors (TIS), including its high quantum efficiency (> 65%), large well-depth, and low noise. We summarize MIRAC-5’s important capabilities, including prospects for obtaining the first continuum mid-infrared measurements for several gas giants and the first 10.2-10.8 micron NH3 detection in the atmosphere of the warm companion GJ 504b (Teff ~ 550 K) within 8 hours of observing time. Finally, we describe plans for future upgrades to MIRAC-5 such as adding a coronagraph. MIRAC5 will be commissioned on the MMT utilizing the new MAPS AO system in late 2022 with plans to move to Magellan with the MagAO system in the future.
The MagAO-X instrument is an extreme adaptive optics system for high-contrast imaging at visible- and near-infrared wavelengths on the Magellan Clay Telescope. A central component of this system is a 2040-actuator microelectromechanical deformable mirror (DM) from Boston Micromachines Corp. that operates at 3.63 kHz for high-order wavefront control (the tweeter). Two additional DMs from ALPAO perform the low-order (the woofer) and non-common-path science-arm wavefront correction (the NCPC DM). Prior to integration with the instrument, we characterized these devices using a Zygo Verifire Interferometer to measure each DM surface. We present the results of the characterization effort here, demonstrating the ability to drive the tweeter to a flat of 6.9 nm root-mean-square (RMS) surface (and 0.56 nm RMS surface within its control bandwidth), the woofer to 2.2-nm RMS surface, and the NCPC DM to 2.1-nm RMS surface over the MagAO-X beam footprint on each device. Using focus-diversity phase retrieval on the MagAO-X science cameras to estimate the internal instrument wavefront error, we further show that the integrated DMs correct the instrument WFE to 18.7 nm RMS, which, combined with a 11.7% pupil amplitude RMS, produces a Strehl ratio of 0.94 at Hα.
MagAO-X is a new “extreme” adaptive optics system for the Magellan Clay 6.5 m telescope which began commissioning in December, 2019. MagAO-X is based around a 2040 actuator deformable mirror, controlled by a pyramid wavefront sensor operating at up to 3.6 kHz. When fully optimized, MagAO-X will deliver high Strehls (< 70%), high resolution (19 mas), and high contrast (< 1 × 10−4) at Hα (656 nm). We present a brief review of the instrument design and operations, and then report on the results of the first-light run.
Our past GAPplanetS survey over the last 5 years with the MagAO visible AO system discovered the first examples of accreting protoplanets (by direct observation of H-alpha emission). Examples include LkCa15 b (Sallum et al. 2015) and PDS70 b (Wagner et al. 2018). In this paper we review the science performance of the newly (Dec. 2019) commissioned MagAO-X extreme AO system. In particular, we use the vAPP coronagraphic contrasts measured during MagAO-X first light. We use the Massive Accreting Gap (MAG) protoplanet model of Close 2020 to predict the H-alpha contrasts of 19 of the best transitional disk systems (ages 1-5 Myr) for the direct detection of H-alpha from accretion of hydrogen onto these protoplanets. The MAG protoplanet model applied to the observed first light MagAO-X contrasts predict a maximum yield of 46±7 planets from 19 stars (42 of these planets would be new discoveries). This suggests that there is a large, yet, unexplored reservoir of protoplanets that can be discovered with an extreme AO coronagraphic survey of 19 of the best transitional disk systems. Based on our first light contrasts we predict a healthy yield of protoplanets from our MaxProtoPlanetS survey of 19 transitional disks with MagAO-X.
MAPS, MMT Adaptive optics exoPlanet characterization System, is the upgrade of the adaptive optics system for 6.5-m MMT. It is an NSF MSIP-funded project that includes developing an adaptive-secondary mirror, visible and near-infrared pyramid wavefront sensors, and the upgrade of Arizona infrared imager and echelle spectrograph (ARIES) and MMT High Precision Imaging Polarimeter (MMTPol) science cameras. This paper will present the design and development of the visible pyramid wavefront sensor, VPWFS. It consists of an acquisition camera, a fast-steering tip-tilt modulation mirror, a pyramid, a pupil imaging triplet lens, and a low noise and high-speed frame rate based CCID75 camera. We will report on hardware and software, present the laboratory characterization results of individual subsystems, and outline the on-sky commissioning plan.
The MMT Adaptive optics exoPlanet characterization System (MAPS) is a broad overhaul and upgrade of AO instrumentation at the 6.5-m MMT observatory, from deformable secondary mirror, through pyramid wavefront sensors in both the visible and near-infrared, to improved science cameras. MAPS is an NSF MSIP-funded program whose ultimate goal is a facility optimized for exoplanet characterization. Here we describe the laboratory testing and calibration of one MAPS component: the refurbished MMT adaptive secondary mirror (ASM). The new ASM includes a complete redesign of electronics and actuators, including simplified hub-level electronics and digital electronics incorporated into the actuators themselves. The redesign reduces total power to ⪅300W, from the original system’s 1800W, which in turn allows us to eliminate liquid cooling at the hub with no loss of performance. We present testing strategies, results, and lessons learned from laboratory experience with the MAPS ASM. We discuss calibrations first on the level of individual actuators, including capacitive position sensing, force response function, and individual closed-loop position control with an improved control law. We then describe investigations into the full ASM system – hub, actuators, thin shell, and human – to understand how to optimize interactions between components for dynamical shape control using a feedforward matrix. Finally, we present our results in the form of feedforward matrix and control law parameters that successfully produce a desired mirror surface within 1ms settling time.
We are upgrading and refurbishing the first-generation adaptive-secondary mirror (ASM)-based AO system on the 6.5-m MMT in Arizona, in an NSF MSIP-funded program that will create a unique facility specialized for exoplanet characterization. This update includes a third-generation ASM with embedded electronics for low power consumption, two pyramid wavefront sensors (optical and near-IR), and an upgraded ARIES science camera for high-resolution spectroscopy (HRS) from 1-5 μm and MMT-POL science camera for sensitive polarization mapping. Digital electronics have been incorporated into each of the 336 actuators, simplifying hub-level electronics and reducing the total power to 300 W, down from 1800 W in the legacy system — reducing cooling requirements from active coolant to passive ambient cooling. An improved internal control law allows for electronic damping and a faster response. The dual pyramid wavefront sensors allow for a choice between optical or IR wavefront sensing depending on guide star magnitude, color, and extinction. The HRS upgrade to ARIES enables crosscorrelation of molecular templates to extract atmospheric parameters of exoplanets. The combination of these upgrades creates a workhorse instrument for exoplanet characterization via AO and HRS to separate planets from their host stars, with broad wavelength coverage and polarization to probe a range of molecular species in exoplanet atmospheres.
Betelgeuse has experienced a sudden shift in its brightness and dimmed mysteriously. This is likely caused by a hot blob of plasma ejected from Betelgeuse and then cooled to obscuring dust. If true, it is a remarkable opportunity to directly witness the formation of dust around a red supergiant star. Today's optical telescope facilities are not optimized for monitoring the Betelgeuse surface, so in this work, we propose a low-cost optical interferometer. The facility will consist of 12 x 4 inch optical telescopes mounted to the surface of a large radio dish for model-independent aperture synthesis imaging; polarization-maintaining single-mode fibers will carry the coherent beams from the individual optical telescopes to an all-in-one beam combiner. A fast steering mirror assisted fiber injection system guides the flux into fibers. A metrology system senses vibration-induced piston errors in optical fibers, and these errors are corrected using fast-steering delay lines. We will present the design.
PHASECam is the fringe tracker for the Large Binocular Telescope Interferometer (LBTI). It is a near-infrared camera that is used to measure both tip/tilt and fringe phase variations between the two adaptive optics-corrected apertures of the Large Binocular Telescope (LBT). Tip/tilt and phase sensing are currently performed in the H (1.65 μm) and K (2.2 μm) bands at 1 kHz, but only the K-band phase telemetry is used to send corrections to the system in order to maintain fringe coherence and visibility. However, due to the cyclic nature of the fringe phase, only the phase, modulo 360 deg, can be measured. PHASECam’s phase unwrapping algorithm, which attempts to mitigate this issue, occasionally fails in cases of fast, large phase variations or low signal-to-noise ratio. This can cause a fringe jump in which case the optical path difference correction will be incorrect by a wavelength. This can currently be manually corrected by the operator. However, as the LBTI commissions further modes that require robust, active phase control and for which fringe jumps are harder to detect, including multiaxial (Fizeau) interferometry and dual-aperture nonredundant aperture masking interferometry, a more reliable and automated solution is desired. We present a multiwavelength method of fringe jump capture and correction that involves direct comparison between the K-band and H-band phase telemetry. We demonstrate the method utilizing archival PHASECam telemetry, showing it provides a robust, reliable way of detecting fringe jumps that can potentially recover a significant fraction of the data lost to them.
The Large Binocular Telescope Interferometer (LBTI) has the longest baseline in the world|22.7 m|for performing astronomical interferometry in Fizeau mode, which involves beam combination in a focal plane and preserves a wide field-of-view. LBTI can operate in this mode at wavelengths of 1.5-5 and 8-12 μm, making it a unique platform for carrying out high-resolution imaging of circumstellar disks, and possibly searches for planets, in the thermal infrared. Over the past five years, LBTI has carried out a considerable number of interferometric observations by combining the beams near a pupil plane to carry out nulling interferometry. This mode is useful for measuring small luminosity level offsets, such as those of exozodiacal dust disks. The Fizeau mode, by contrast, is more useful for generating an image of the target because it has more uv plane coverage. However, the Fizeau mode is still in an ongoing process of commissioning. Sensitive Fizeau observations require active phase control, increased automation, and the removal of non-common-path (NCP) differential aberrations. These maximize the fringe contrast, enable longer integrations, and reduce time overheads. We are in the process of writing a correction loop to remove NCP aberrations, and have carried out tests on old and synthetic data. We have also carried out on-sky Fizeau engineering tests in 2018B and 2019A. In this article, we share lessons learned and strategies developed as a result of these tests.
The presence of large amounts of dust in the habitable zones of nearby stars is a significant obstacle for future exo-Earth imaging missions. We executed the HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey to determine the typical amount of such exozodiacal dust around a sample of nearby main sequence stars. The majority of the data have been analyzed and we present here an update of our ongoing work. Nulling interferometry in N band was used to suppress the bright stellar light and to detect faint, extended circumstellar dust emission. We present an overview of the latest results from our ongoing work. We find seven new N band excesses in addition to the high confidence confirmation of three that were previously known. We find the first detections around Sun-like stars and around stars without previously known circumstellar dust. Our overall detection rate is 23%. The inferred occurrence rate is comparable for early type and Sun-like stars, but decreases from 71+11 -20% for stars with previously detected mid- to far-infrared excess to 11+9 -4% for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal luminosity function of the dust, we find upper limits on the median dust level around all stars without previously known mid to far infrared excess of 11.5 zodis at 95% confidence level. The corresponding upper limit for Sun-like stars is 16 zodis. An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a corresponding limit of 7.5 zodis. We provide important new insights into the occurrence rate and typical levels of habitable zone dust around main sequence stars. Exploiting the full range of capabilities of the LBTI provides a critical opportunity for the detailed characterization of a sample of exozodiacal dust disks to understand the origin, distribution, and properties of the dust.
The challenges of high contrast imaging (HCI) for detecting exoplanets for both ground and space applications can be met with extreme adaptive optics (ExAO), a high-order adaptive optics system that performs wavefront sensing (WFS) and correction at high speed. We describe 2 ExAO optical system designs, one each for ground- based telescopes and space-based missions, and examine them using the angular spectrum Fresnel propagation module within the Physical Optics Propagation in Python (POPPY) package. We present an end-to-end (E2E) simulation of the MagAO-X instrument, an ExAO system capable of delivering 6x10-5 visible-light raw contrast for static, noncommon path aberrations without atmosphere. We present an E2E simulation of a laser guidestar (LGS) companion spacecraft testbed demonstration, which uses a remote beacon to increase the signal available for WFS and control of the primary aperture segments of a future large space telescope, providing of order 10 factor improvement for relaxing observatory stability requirements.
Despite promising astrometric signals, to date there has been no success in direct imaging of a hypothesized third member of the Sirius system. Using the Clio instrument and MagAO adaptive optics system on the Magellan Clay 6.5 m telescope, we have obtained extensive imagery of Sirius through a vector apodizing phase plate (vAPP) coronagraph in a narrowband filter at 3.9 microns. The vAPP coronagraph and MagAO allow us to be sensitive to planets much less massive than the limits set by previous non-detections. However, analysis of these data presents challenges due to the target’s brightness and unique characteristics of the instrument. We present a comparison of dimensionality reduction techniques to construct background illumination maps for the whole detector using the areas of the detector that are not dominated by starlight. Additionally, we describe a procedure for sub-pixel alignment of vAPP data using a physical-optics-based model of the coronagraphic PSF.
MagAO-X is an entirely new extreme adaptive optics system for the Magellan Clay 6.5 m telescope, funded by the NSF MRI program starting in Sep 2016. The key science goal of MagAO-X is high-contrast imaging of accreting protoplanets at Hα. With 2040 actuators operating at up to 3630 Hz, MagAO-X will deliver high Strehls (> 70%), high resolution (19 mas), and high contrast (< 1 × 10-4 ) at Hα (656 nm). We present an overview of the MagAO-X system, review the system design, and discuss the current project status.
The Active optics, Guiding, and Wavefront Sensing system (AGWS), currently being designed by SAO, will use J-band dispersed fringe sensors (DFS) to phase the GMT to a fraction of an imaging wavelength. These phasing sensors will use off-axis guide stars to measure phase shifts at each of 12 segment boundaries. The fringes produced at each boundary will be dispersed in the perpendicular direction using an array of high-index doublet prisms. Inter-segment phase shifts will appear as tilts in the dispersed fringes, which can be measured in the Fourier domain. In order to avoid atmospheric blurring of the fringes, we require a J-band detector capable of fast, low-noise readout, which mandates the use of a SAPHIRA e-APD array. We built a DFS prototype that we tested on-sky at the Magellan Clay telescope behind the MagAO adaptive optics system in May 2018.
We review astronomical results in the visible (λ<1μm) with adaptive optics and note the status the MagAO system and the recent upgrade to visible camera’s Simultaneous/Spectra Differential Imager (SDI+) mode. Since mid- 2013 there has been a rapid increase visible AO with over 50 refereed science papers published in just 2015-2016 timeframe. Currently there are productive small (D < 2 m) visible light AO telescopes like the UV-LGS Robo-AO system (Baranec, et al. 2016). The largest (D=8m) telescope to achieve regular visible AO science is SPHERE/ZIMPOL. ZIMPOL is a polarimeter fed by the ~1.2 kHz SPHERE ExAO system (Fusco et al. 2016). ZIMPOL’s ability to differentiate scattered polarized light from starlight allows the sensitive detection of circumstellar disks, stellar surfaces, and envelopes of evolved AGB stars. The main focus of this paper is another large (D=6.5m Magellan telescope) AO system (MagAO) which has been very productive in the visible as well (particularly at the H−alpha emission line). MagAO is an advanced Adaptive Secondary Mirror (ASM) AO system at the Magellan in Chile. This ASM secondary has 585 actuators with < 1 msec response times (0.7 ms typically). MagAO utilizes a 1 kHz pyramid wavefront sensor (PWFS). The relatively small actuator pitch (~22 cm/subap, 300 modes, upgraded to 30 pix dia. PWFS) allows moderate Strehls to be obtained in the visible (0.63-1.05 microns). Long exposures (60s) achieve <30mas resolutions and 30% Strehls at 0.62 microns (r') with the VisAO camera (0.5-1.0 μm) in 0.5” seeing with bright R ≤ 9 mag stars (~10% Strehls can be obtained on fainter R~12 mag guide stars). Differential Spectral Imaging (SDI) at H-alpha has been very important for accreting exoplanet detection. There is also a 1-5micron science camera (Clio; Morzinski et al. 2016). These capabilities have led to over 35 MagAO refereed science publications. Here we review the key steps to having good performance in the visible and review the exciting new AO visible science opportunities and science results in the fields of: exoplanet detection; circumstellar and protoplanetary disks; young stars; AGB stars; emission line jets; and stellar surfaces. The recent rapid increase in the scientific publications and power of visible AO is due to the maturity of the next-generation of AO systems and our new ability probe circumstellar regions with very high (10-30 mas) spatial resolutions that would otherwise require much larger (<10m) diameter telescopes in the infrared.
The Magellan extreme adaptive optics (MagAO-X) instrument is a new extreme adaptive optics (ExAO) system designed for operation in the visible to near-IR which will deliver high contrast-imaging capabilities. The main AO system will be driven by a pyramid wavefront sensor (PyWFS); however, to mitigate the impact of quasi-static and non-common path (NCP) aberrations, focal plane wavefront sensing (FPWFS) in the form of low-order wavefront sensing (LOWFS) and spatial linear dark field control (LDFC) will be employed behind a vector apodizing phase plate (vAPP) coronagraph using rejected starlight at an intermediate focal plane. These techniques will allow for continuous high-contrast imaging performance at the raw contrast level delivered by the vAPP coronagraph ( 6 x 10-5). We present simulation results for LOWFS and spatial LDFC with a vAPP coronagraph, as well as laboratory results for both algorithms implemented with a vAPP coronagraph at the University of Arizona Extreme Wavefront Control Lab.
The Epsilon Eridani system is a star system ~10 ly away predicted to be similar to our solar system, making it a particularly interesting target for exoplanet detection. A Jupiter-like exoplanet has been predicted at 1.88 arcsec using radial velocity techniques, and an outer debris disk has been imaged at 35 - 90 AU with Spitzer and CSO observations. We present a preliminary survey of the inner system using the MagAO instrument with the Magellan Clay telescope in Chile. We apply and evaluate the Karhunen-Loeve Image Projection technique, which estimates the point spread function (PSF) of the central star for high-contrast imaging using Principal Component Analysis (PCA). We perform this analysis by adapting the pyKLIP package, which was developed for analyzing data from the Gemini Planet Imager instrument, to be used with data from the MagAO/VisAO instrument.
The GMT is an aplanatic Gregorian telescope consisting of 7 primary and secondary mirror segments that must be phased to within a fraction of an imaging wavelength to allow the 25.4 meter telescope to reach its diffraction limit. When operating in Laser Tomographic Adaptive Optics (LTAO) mode, on-axis guide stars will not be available for segment phasing. In this mode, the GMT’s Acquisition, Guiding, and Wavefront Sensing system (AGWS) will deploy four pickoff probes to acquire natural guide stars in a 6-10 arcmin annular FOV for guiding, active optics, and segment phasing. The phasing sensor will be able to measure piston phase differences between the seven primary/secondary pairs of up to 50 microns with an accuracy of 50 nm using a J-band dispersed fringe sensor. To test the dispersed fringe sensor design and validate the performance models, SAO has built and commissioned a prototype phasing sensor on the Magellan Clay 6.5 meter telescope. This prototype uses an aperture mask to overlay 6 GMT-sized segment gap patterns on the Magellan 6.5 meter primary mirror reimaged pupil. The six diffraction patterns created by these subaperture pairs are then imaged with a lenslet array and dispersed with a grism. An on-board phase shifter has the ability to simulate an arbitrary phase shift within subaperture pairs. The prototype operates both on-axis and 6 arcmin off-axis either with AO correction from the Magellan adaptive secondary MagAO system on or off in order to replicate as closely as possible the conditions expected at the GMT.
Astronomical data sets are growing ever larger, and the area of high contrast imaging of exoplanets is no exception. With the advent of fast, low-noise detectors operating at 10 to 1000 Hz, huge numbers of images can be taken during a single hours-long observation. High frame rates offer several advantages, such as improved registration, frame selection, and improved speckle calibration. However, advanced image processing algorithms are computationally challenging to apply. Here we describe a parallelized, cloud-based data reduction system developed for the Magellan Adaptive Optics VisAO camera, which is capable of rapidly exploring tens of thousands of parameter sets affecting the Karhunen-Loève image processing (KLIP) algorithm to produce high-quality direct images of exoplanets. We demonstrate these capabilities with a visible wavelength high contrast data set of a hydrogen-accreting brown dwarf companion.
Transition disks, protoplanetary disks with inner clearings, are promising objects in which to directly image forming planets. The high contrast imaging technique of non-redundant masking is well posed to detect planetary mass companions at several to tens of AU in nearby transition disks. We present non-redundant masking observations of the T Cha and LkCa 15 transition disks, both of which host posited sub-stellar mass companions. However, due to a loss of information intrinsic to the technique, observations of extended sources (e.g. scattered light from disks) can be misinterpreted as moving companions. We discuss tests to distinguish between these two scenarios, with applications to the T Cha and LkCa 15 observations. We argue that a static, forward-scattering disk can explain the T Cha data, while LkCa 15 is best explained by multiple orbiting companions.
The Large Binocular Telescope Interferometer (LBTI) is a high spatial resolution instrument developed for coherent imaging and nulling interferometry using the 14.4 m baseline of the 2×8.4 m LBT. The unique telescope design, comprising of the dual apertures on a common elevation-azimuth mount, enables a broad use of observing modes. The full system is comprised of dual adaptive optics systems, a near-infrared phasing camera, a 1-5 μm camera (called LMIRCam), and an 8-13 μm camera (called NOMIC). The key program for LBTI is the Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS), a survey using nulling interferometry to constrain the typical brightness from exozodiacal dust around nearby stars. Additional observations focus on the detection and characterization of giant planets in the thermal infrared, high spatial resolution imaging of complex scenes such as Jupiter's moon, Io, planets forming in transition disks, and the structure of active Galactic Nuclei (AGN). Several instrumental upgrades are currently underway to improve and expand the capabilities of LBTI. These include: Improving the performance and limiting magnitude of the parallel adaptive optics systems; quadrupling the field of view of LMIRcam (increasing to 20"x20"); adding an integral field spectrometry mode; and implementing a new algorithm for path length correction that accounts for dispersion due to atmospheric water vapor. We present the current architecture and performance of LBTI, as well as an overview of the upgrades.
The next generation of extremely large telescopes (ELTs) have the potential to image habitable rocky planets, if suitably optimized. This will require the development of fast high order "extreme" adaptive optics systems for the ELTs. Located near the excellent site of the future GMT, the Magellan AO system (MagAO) is an ideal on-sky testbed for high contrast imaging development. Here we discuss planned upgrades to MagAO. These include improvements in WFS sampling (enabling correction of more modes) and an increase in speed to 2000 Hz, as well as an H2RG detector upgrade for the Clio infrared camera. This NSF funded project, MagAO-2K, is planned to be on-sky in November 2016 and will significantly improve the performance of MagAO at short wavelengths. Finally, we describe MagAO-X, a visible-wavelength extreme-AO "afterburner" system under development. MagAO-X will deliver Strehl ratios of over 80% in the optical and is optimized for visible light coronagraphy.
Frequency-based analysis and comparisons of tip-tilt on-sky data registered with 6.5 Magellan Telescope Adaptive Optics (MagAO) system on April and Oct 2014 was performed. Twelve tests are conducted under different operation conditions in order to observe the influence of system instrumentation (such as fans, pumps and louvers). Vibration peaks can be detected, power spectral densities (PSDs) are presented to reveal their presence. Instrumentation-induced resonances, close-loop gain and future challenges in vibrations mitigation techniques are discussed.
KEYWORDS: Adaptive optics, Control systems, Sensors, Telescopes, Adaptive optics, Control systems, Fluctuations and noise, Turbulence, Charge-coupled devices, Device simulation, Signal processing, Data modeling
The Magellan Telescope Adaptive Optics System (MagAO) is subject to resonance effects induced by elements within the system instrumentation, such as fans and cooling pumps. Normalized PSDs are obtained through frequency-based analysis of closed-loop on-sky data, detecting and measuring vibration effects. Subsequently, a space-state model for the AO loop is obtained, using a standard AO loop scheme with an integrator-based controller and including the vibration effects as disturbances. Finally, a new control alternative is proposed, focusing on residual phase variance minimization through the design and simulation of an optimal LQG control approach.
”MagAO" is the adaptive optics instrument at the Magellan Clay telescope at Las Campanas Observatory, Chile. MagAO has a 585-actuator adaptive secondary mirror and 1000-Hz pyramid wavefront sensor, operating on natural guide stars from R-magnitudes of -1 to 15. MagAO has been in on-sky operation for 166 nights since installation in 2012. MagAO's unique capabilities are simultaneous imaging in the visible and infrared with VisAO and Clio, excellent performance at an excellent site, and a lean operations model. Science results from MagAO include the first ground-based CCD image of an exoplanet, demonstration of the first accreting protoplanets, discovery of a new wide-orbit exoplanet, and the first empirical bolometric luminosity of an exoplanet. We describe the status, report the AO performance, and summarize the science results. New developments reported here include color corrections on red guide stars for the wavefront sensor; a new field stop stage to facilitate VisAO imaging of extended sources; and eyepiece observing at the visible-light diffraction limit of a 6.5-m telescope. We also discuss a recent hose failure that led to a glycol coolant leak, and the recovery of the adaptive secondary mirror (ASM) after this recent (Feb. 2016) incident.
We review astronomical results in the visible (λ<1μm) with adaptive optics. Other than a brief period in the early 1990s, there has been little astronomical science done in the visible with AO until recently. The most productive visible AO system to date is our 6.5m Magellan telescope AO system (MagAO). MagAO is an advanced Adaptive Secondary system at the Magellan 6.5m in Chile. This secondary has 585 actuators with < 1 msec response times (0.7 ms typically). We use a pyramid wavefront sensor. The relatively small actuator pitch (~23 cm/subap) allows moderate Strehls to be obtained in the visible (0.63-1.05 microns). We use a CCD AO science camera called “VisAO”. On-sky long exposures (60s) achieve <30mas resolutions, 30% Strehls at 0.62 microns (r') with the VisAO camera in 0.5” seeing with bright R < 8 mag stars. These relatively high visible wavelength Strehls are made possible by our powerful combination of a next generation ASM and a Pyramid WFS with 378 controlled modes and 1000 Hz loop frequency. We'll review the key steps to having good performance in the visible and review the exciting new AO visible science opportunities and refereed publications in both broad-band (r,i,z,Y) and at Halpha for exoplanets, protoplanetary disks, young stars, and emission line jets. These examples highlight the power of visible AO to probe circumstellar regions/spatial resolutions that would otherwise require much larger diameter telescopes with classical infrared AO cameras.
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.
KEYWORDS: Gemini Planet Imager, Distortion, Iterated function systems, Monte Carlo methods, Planets, Stars, Coronagraphy, Calibration, Telescopes, Point spread functions
We present the results of both laboratory and on sky astrometric characterization of the Gemini Planet Imager (GPI). This characterization includes measurement of the pixel scale* of the integral field spectrograph (IFS), the position of the
detector with respect to north, and optical distortion. Two of these three quantities (pixel scale and distortion) were
measured in the laboratory using two transparent grids of spots, one with a square pattern and the other with a random pattern. The pixel scale in the laboratory was also estimate using small movements of the artificial star unit (ASU) in the
GPI adaptive optics system. On sky, the pixel scale and the north angle are determined using a number of known binary or multiple systems and Solar System objects, a subsample of which had concurrent measurements at Keck Observatory. Our current estimate of the GPI pixel scale is 14.14 ± 0.01 millarcseconds/pixel, and the north angle is -1.00 ± 0.03°. Distortion is shown to be small, with an average positional residual of 0.26 pixels over the field of view, and is corrected using a 5th order polynomial. We also present results from Monte Carlo simulations of the GPI Exoplanet Survey (GPIES) assuming GPI achieves ~1 milliarcsecond relative astrometric precision. We find that with this precision, we
will be able to constrain the eccentricities of all detected planets, and possibly determine the underlying eccentricity
distribution of widely separated Jovians.
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its ~130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope’s overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L’ (3.8 μm), as opposed to the shorter wavelength near-infrared bands (1-2.4 μm) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent (~0.1-1 Gyr) stars. LEECH’s contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5μm in preparation for JWST.
One of the primary goals of exoplanet science is to find and characterize habitable planets, and direct imaging will play a key role in this effort. Though imaging a true Earth analog is likely out of reach from the ground, the coming generation of giant telescopes will find and characterize many planets in and near the habitable zones (HZs) of nearby stars. Radial velocity and transit searches indicate that such planets are common, but imaging them will require achieving extreme contrasts at very small angular separations, posing many challenges for adaptive optics (AO) system design. Giant planets in the HZ may even be within reach with the latest generation of high-contrast imagers for a handful of very nearby stars. Here we will review the definition of the HZ, and the characteristics of detectable planets there. We then review some of the ways that direct imaging in the HZ will be different from the typical exoplanet imaging survey today. Finally, we present preliminary results from our observations of the HZ of α Centauri A with the Magellan AO system’s VisAO and Clio2 cameras.
MagAO is the new adaptive optics system with visible-light and infrared science cameras, located on the 6.5-m Magellan “Clay” telescope at Las Campanas Observatory, Chile. The instrument locks on natural guide stars (NGS) from 0th to 16th R-band magnitude, measures turbulence with a modulating pyramid wavefront sensor binnable from 28×28 to 7×7 subapertures, and uses a 585-actuator adaptive secondary mirror (ASM) to provide at wavefronts to the two science cameras. MagAO is a mutated clone of the similar AO systems at the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. The high-level AO loop controls up to 378 modes and operates at frame rates up to 1000 Hz. The instrument has two science cameras: VisAO operating from 0.5-1μm and Clio2 operating from 1-5 μm. MagAO was installed in 2012 and successfully completed two commissioning runs in 2012-2013. In April 2014 we had our first science run that was open to the general Magellan community. Observers from Arizona, Carnegie, Australia, Harvard, MIT, Michigan, and Chile took observations in collaboration with the MagAO instrument team. Here we describe the MagAO instrument, describe our on-sky performance, and report our status as of summer 2014.
To image faint substellar companions obscured by the stellar halo and speckles, scattered light from the bright primary star must be removed in hardware or software. We apply the "locally-optimized combination of images" (LOCI) algorithm to 1-minute Keck Observatory snapshots of GKM dwarfs in the Hyades using source diversity to determine the most likely PSF. We obtain a mean contrast of 10-2 at 0".01, 10-4 at <1", and 10-5 at 5". New brown dwarf and low-mass stellar companions to Hyades primaries are found in a third of the 84 targeted systems. This campaign shows the efficacy of LOCI on snapshot imaging as well as on bright wide binaries with off-axis LOCI, reaching contrasts sufficient for imaging 625-Myr late-L/early-T dwarfs purely in post-processing.
We present laboratory results of the closed-loop performance of the Magellan Adaptive Optics (AO) Adaptive
Secondary Mirror (ASM), pyramid wavefront sensor (PWFS), and VisAO visible adaptive optics camera. The Magellan
AO system is a 585-actuator low-emissivity high-throughput system scheduled for first light on the 6.5 meter Magellan
Clay telescope in November 2012. Using a dichroic beamsplitter near the telescope focal plane, the AO system will be
able to simultaneously perform visible (500-1000 nm) AO science with our VisAO camera and either 10 μm or 3-5 μm
science using either the BLINC/MIRAC4 or CLIO cameras, respectively. The ASM, PWS, and VisAO camera have
undergone final system tests in the solar test tower at the Arcetri Institute in Florence, Italy, reaching Strehls of 37% in
i'-band with 400 modes and simulated turbulence of 14 cm ro at v-band. We present images and test results of the assembled VisAO system, which includes our prototype advanced Atmospheric Dispersion Corrector (ADC), prototype
calcite Wollaston prisms for SDI imaging, and a suite of beamsplitters, filters, and other optics. Our advanced ADC
performs in the lab as designed and is a 58% improvement over conventional ADC designs. We also present images and
results of our unique Calibration Return Optic (CRO) test system and the ASM, which has successfully run in closedloop
at 1kHz. The CRO test is a retro reflecting optical test that allows us to test the ASM off-sky in close-loop using an
artificial star formed by a fiber source.
The Magellan AO system combines a pyramid wavefront sensor and high-order adaptive secondary mirror, and
will see first light on the Magellan Clay telescope in November 2012. With a 24 cm projected actuator pitch,
this powerful system will enable good correction in the optical (0.5 to 1 μm). Realistic laboratory testing has
produced Strehl ratios greater than 40% in i’ (0.765 μm) on bright simulated stars. On fainter stars our visible
AO camera, VisAO, will work in the partially corrected regime with only short moments of good correction.
We have developed a form of lucky imaging, called real time frame selection, which uses a fast shutter to block
moments of bad correction, and quickly opens the shutter when the correction is good, enabling long integrations
on a conventional CCD while maximizing Strehl ratio and resolution. The decision to open or shut is currently
based on reconstructed WFS telemetry. Here we report on our implementation and testing of this technique in
the Arcetri test tower in Florence, Italy, where we showed that long exposure i’ Strehl could be improved from
16% to 26% when the selection threshold was set to the best 10% of instantaneous Strehl.
The heart of the 6.5 Magellan AO system (MagAO) is a 585 actuator adaptive secondary
mirror (ASM) with <1 msec response times (0.7 ms typically). This adaptive secondary will
allow low emissivity and high-contrast AO science. We fabricated a high order (561 mode)
pyramid wavefront sensor (similar to that now successfully used at the Large Binocular
Telescope). The relatively high actuator count (and small projected ~23 cm pitch) allows
moderate Strehls to be obtained by MagAO in the “visible” (0.63-1.05 μm). To take advantage
of this we have fabricated an AO CCD science camera called "VisAO". Complete “end-to-end”
closed-loop lab tests of MagAO achieve a solid, broad-band, 37% Strehl (122 nm rms) at 0.76
μm (i’) with the VisAO camera in 0.8” simulated seeing (13 cm ro at V) with fast 33 mph
winds and a 40 m Lo locked on R=8 mag artificial star. These relatively high visible
wavelength Strehls are enabled by our powerful combination of a next generation ASM and a
Pyramid WFS with 400 controlled modes and 1000 Hz sample speeds (similar to that used
successfully on-sky at the LBT). Currently only the VisAO science camera is used for lab
testing of MagAO, but this high level of measured performance (122 nm rms) promises even
higher Strehls with our IR science cameras. On bright (R=8 mag) stars we should achieve very
high Strehls (>70% at H) in the IR with the existing MagAO Clio2 (λ=1-5.3 μm) science
camera/coronagraph or even higher (~98% Strehl) the Mid-IR (8-26 microns) with the existing
BLINC/MIRAC4 science camera in the future. To eliminate non-common path vibrations,
dispersions, and optical errors the VisAO science camera is fed by a common path advanced
triplet ADC and is piggy-backed on the Pyramid WFS optical board itself. Also a high-speed
shutter can be used to block periods of poor correction. The entire system passed CDR in June
2009, and we finished the closed-loop system level testing phase in December 2011. Final
system acceptance (“pre-ship” review) was passed in February 2012. In May 2012 the entire
AO system is was successfully shipped to Chile and fully tested/aligned. It is now in storage in
the Magellan telescope clean room in anticipation of “First Light” scheduled for December
2012. An overview of the design, attributes, performance, and schedule for the Magellan AO
system and its two science cameras are briefly presented here.
Micro-electro-mechanical systems (MEMS) technology can provide for deformable mirrors (DMs) with excellent
performance within a favorable economy of scale. Large MEMS-based astronomical adaptive optics (AO) systems
such as the Gemini Planet Imager are coming on-line soon. As MEMS DM end-users, we discuss our decade of
practice with the micromirrors, from inspecting and characterizing devices to evaluating their performance in
the lab. We also show MEMS wavefront correction on-sky with the "Villages" AO system on a 1-m telescope,
including open-loop control and visible-light imaging. Our work demonstrates the maturity of MEMS technology
for astronomical adaptive optics.
At the University of California's Lick Observatory, we have implemented an on-sky testbed for next-generation
adaptive optics (AO) technologies. The Visible-Light Laser Guidestar Experiments instrument (ViLLaGEs)
includes visible-light AO, a micro-electro-mechanical-systems (MEMS) deformable mirror, and open-loop control
of said MEMS on the 1-meter Nickel telescope at Mt. Hamilton. (Open-loop in this sense refers to the MEMS
being separated optically from the wavefront sensing path; the MEMS is still included in the control loop.) Future
upgrades include predictive control with wind estimation and pyramid wavefront sensing. Our unique optical
layout allows the wavefronts along the open- and closed-loop paths to be measured simultaneously, facilitating
comparison between the two control methods. In this paper we evaluate the performance of ViLLaGEs in openand
closed-loop control, finding that both control methods give equivalent Strehl ratios of up to ~ 7% in I-band
and similar rejection of temporal power. Therefore, we find that open-loop control of MEMS on-sky is as effective
as closed-loop control. Furthermore, after operating the system for three years, we find MEMS technology to
function well in the observatory environment. We construct an error budget for the system, accounting for 130
nm of wavefront error out of 190 nm error in the science-camera PSFs. We find that the dominant known term
is internal static error, and that the known contributions to the error budget from open-loop control (MEMS
model, position repeatability, hysteresis, and WFS linearity) are negligible.
We present preliminary findings on the characteristic behavior and initial performance of Boston Micromachine
Corporations' (BMC) 4096-actuator micro-electrical mechanical systems (MEMS) deformable mirror (DM). This
device is examined for its application in the Gemini Planet Imager high-contrast adaptive optics (AO) system. It is
also being considered for use in next generation AO systems on the extremely large telescopes. Testing of this device
has been in progress at the Laboratory for Adaptive Optics (LAO) on the Extreme Adaptive Optics (ExAO) testbed
in experiments designed to qualify performance for imaging extrasolar planets. In this paper we present first test
results including actuator stroke (3.0 microns at 200 V), individual actuator RMS surface (10.3 nm surface), actuator
yield for two DM arrays (94.4% and 98.8%), actuator crosstalk (no more than 32%), stroke at the highest spatial
frequency (1.2 nm surface), and sub-nanometer closed loop flattening capabilities over a 30-actuator diameter.
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 Gemini Planet Imager (GPI) is currently in production for the Gemini Telescope in Chile. This instrument
will directly image young jovian exoplanets, aided by a micro-electrical mechanical systems (MEMS) deformable
mirror (DM). Boston Micromachines MEMS mirrors operate thousands of actuators to provide a well-sampled
correction at high spatial frequencies. However, because MEMS stroke alone is insufficient to fully correct the
atmosphere in the near-IR on an 8-meter telescope, a dual-mirror system is planned for GPI: The MEMS is used
as a 'tweeter' to correct the higher spatial frequencies while a separate 'woofer' DM will be used to correct
the lower frequencies. During operation at GPI, any saturated actuators would scatter starlight into the dark
hole instead of allowing it to be removed coronagraphically; thus, stroke saturation on the MEMS is tolerated
only at the 5-sigma level. In the Laboratory for Adaptive Optics, we test the ability of the MEMS to counter
atmospheric turbulence. The MEMS shape is set to random iterations of woofer-corrected Kolmogorov phase
screens with varying woofer sizes. We find that, for r0 = 10 cm, saturation decreases from several percent
to a few tenths of a percent (∼3-sigma) when using a 100cm-pitch woofer. The MEMS we tested has 0.2 &mgr;m
inter-actuator stroke for a 200V-range. Nonetheless, saturation (when it occurs) appears to be due to low-order
peak-to-valley stroke even in the woofer-corrected case. Gemini characteristically has r0 = 15 cm, so future
work includes extrapolating to find where the 5-sigma saturation level occurs.
We attempt to linearize the output of the Shack-Hartmann wavefront sensor in the ViLLaGEs instrument. ViLLaGEs
(Visible Light Laser Guidestar Experiments) is a MEMS-based Adaptive Optics system on the 1 - meter Nickel
telescope at Lick Observatory meant to provide correction at visible wavelengths with a 9x9 subaperture Hartmann
sensor. We estimate that the open-loop accuracy of ViLLaGEs is ~40 nm. We "calibrate" the Hartmann linearity by
raster scanning a tip/tilt mirror downstream of an internal fiber and inverting the resulting signal, forming a lookup table
of unbiased tilts. From this calibration, we conclude that nonlinearity is a minor effect in the open-loop operation of
ViLLaGEs, on the order of ~15 nm. We show through simulations of Shack-Hartmann sensors that this error is likely
due to an internal pupil mask not physically conjugate to the telescope pupil. We test the resulting lookup table on an
internal "turbulator" in ViLLaGEs, or a rotating plate meant to simulate the wind-driven atmosphere, and find that the
Strehls with and without the lookup table are indistinguishable.
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.
New concepts for astronomical adaptive optics are enabled by use of micro-electrical mechanical systems (MEMS)
deformable mirrors (DMs). Unlike traditional DMs now used in astronomical AO systems, MEMS devices are
smaller, less expensive, and exhibit extraordinarily repeatable actuation. Consequently, MEMS technology
allows for novel configurations, such as multi-object AO, that require open-loop control of multiple DMs. At the
UCO/Lick Observatory Laboratory for Adaptive Optics we are pursuing this concept in part by creating a phaseto-
voltage model for the MEMS DM. We model the surface deflection approximately by the thin-plate equation.
Using this modeling technique, we have achieved open-loop control accuracy in the laboratory to ~13-30 nm
surface rms in response to ~1-3 μm peak-to-valley commands, respectively. Next, high-resolution measurements
of the displacement between actuator posts are compared to the homogeneous solution of the thin-plate equation,
to verify the model's validity. These measurements show that the thin-plate equation seems a plausible approach
to modeling deformations of the top surface down to lateral scales of a tenth actuator spacing. Finally, in order
to determine the physical lower limit to which our model can be expected to be accurate, we conducted a set
of hysteresis experiments with a MEMS. We detect only a sub-nanometer amount of hysteresis of 0.6±0.3 nm
surface over a 160-volt loop. This complements our previous stability and position repeatability measurements,
showing that MEMS DMs actuate to sub-nanometer precision and are hence controllable in open-loop.
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.
As adaptive optics (AO) technology progresses, both wide-field and high-order wavefront correction systems become
reachable. Deformable mirrors (DMs) in these advanced architectures must exhibit exemplary performance
to give low wavefront error. Such DMs must be economically attainable, meet stroke as well as flatness requirements,
and show stable and repeatable actuation. Micro-electrical mechanical systems (MEMS) deformable
mirrors, undergoing testing and characterization in the Laboratory for Adaptive Optics (LAO) at the University
of California at Santa Cruz, show promise on these fronts. In addition to requiring advanced deformable mirror
technology, these progressive AO architectures require advanced DM control algorithms. We therefore present
a formulation for accurate open-loop control of MEMS deformable mirrors. The electrostatic actuators in a
discrete-actuator MEMS device are attached via posts to a thin reflective top plate. The plate itself can be
well-modeled by the thin plate equation. The actuators, although nonlinear in their response to applied voltage
and deformation, are independent of each other except through forces transmitted by the top plate and can be
empirically modeled via a calibration procedure we will describe. In this paper we present the modeling and
laboratory results. So far in the lab we have achieved open loop control to approximately 15 nm accuracy in response to arbitrary
commands of approximately 500 nm amplitude. Open-loop control enables a wealth of new applications for astronomical
adaptive optics instruments, particularly in multi-object integral field spectroscopy, which we will describe.
Current high-contrast "extreme" adaptive optics (ExAO) systems are partially limited by deformable mirror technology. Mirror requirements specify thousands of actuators, all of which must be functional within the clear aperture, and which give nanometer flatness yet micron stroke when operated in closed loop.1 Micro-electrical mechanical-systems (MEMS) deformable mirrors have been shown to meet ExAO actuator yield, wavefront error, and cost considerations. This study presents the performance of Boston Micromachines' 1024-actuator continuous-facesheet MEMS deformable mirrors under tests for actuator stability, position repeatability, and practical operating stroke. To explore whether MEMS actuators are susceptible to temporal variation, a series of long-term stability experiments were conducted. Each actuator was held fixed and the motion over 40 minutes was measured. The median displacement of all the actuators tested was 0.08 nm surface, inclusive of system error. MEMS devices are also appealing for adaptive optics architectures based on open-loop correction. In experiments of actuator position repeatability, 100% of the tested actuators returned repeatedly to their starting point with a precision of < 1 nm surface. Finally, MEMS devices were tested for maximum stroke achieved under application of spatially varying one-dimensional sinusoids. Given a specified amplitude in voltage, the measured stroke was 1 μm surface at the low spatial frequencies, decreasing to 0.2 μm surface for the highest spatial frequency. Stroke varied somewhat linearly as inverse spatial frequency, with a flattening in the relation at the high spatial frequency end.
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.
We have demonstrated that a microelectrical mechanical systems (MEMS) deformable mirror can be flattened to < 1 nm RMS within controllable spatial frequencies over a 9.2-mm aperture making it a viable option for high-contrast adaptive optics systems (also known as Extreme Adaptive Optics). The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. A phase shifting diffraction interferometer (PSDI) measures wavefront errors with sub-nm precision and accuracy for metrology and wavefront control. Consistent flattening, required testing and characterization of the individual actuator response, including the effects of dead and low-response actuators. Stability and repeatability of the MEMS devices was also tested. An error budget for MEMS closed loop performance will summarize MEMS characterization.
"Extreme" adaptive optics systems are optimized for ultra-high contrast applications, such as ground-based extrasolar planet detection. The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. We use a simple optical design to minimize wavefront error and maximize the experimentally achievable contrast. A phase shifting diffraction interferometer (PSDI) measures wavefront errors with sub-nm precision and accuracy for metrology and wavefront control. Previously, we have demonstrated RMS wavefront errors of <1.5 nm and a contrast of >107 over a substantial region using a shaped pupil without a deformable mirror. Current work includes the installation and characterization of a 1024-actuator Micro-Electro-Mechanical-Systems (MEMS) deformable mirror, manufactured by Boston Micro-Machines for active wavefront control. Using the PSDI as the wavefront sensor we have flattened the deformable mirror to <1 nm within the controllable spatial frequencies and measured a contrast in the far field of >106. Consistent flattening required testing and characterization of the individual actuator response, including the effects of dead and low-response actuators. Stability and repeatability of the MEMS devices was also tested. Ultimately this testbed will be used to test all aspects of the system architecture for an extrasolar planet-finding AO system.
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