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.
Adaptive optics (AO) and optical coherence tomography (OCT) are powerful imaging modalities that, when
combined, can provide high-resolution (3.5 μm isotropic), 3-D images of the retina. The AO-OCT system at
UC Davis has demonstrated the utility of this technology for microscopic, volumetric, in vivo retinal imaging.
The current system uses an AOptix bimorph deformable mirror (DM) for low-order, high-stroke correction and
a 140-actuator Boston Micromachines DM for high-order correction. Developments to improve performance or
functionality of the instrument are on-going. Based on previous work in system characterization we have focused
on improved AO control. We present preliminary results and remaining challenges for a newly implemented
Fourier transform reconstructor (FTR). The previously reported error budget analysis is also reviewed and
updated, with consideration of how to improve both the amount of residual error and the robustness of the
system. Careful characterization of the AO system will lead to improved performance and inform the design of
future systems.
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.
Imaging the structure and correlating it with the biochemical content of the retina holds promise for fundamental
research and for clinical applications. Optical coherence tomography (OCT) is commonly used to image the 3D
structure of the retina and while the added functionality of biochemical analysis afforded by Raman scattering
could provide critical molecular signatures for clinicians and researchers, there are many technical challenges to
combining these imaging modalities. We present an ex vivo OCT microscope combined with Raman spectroscopy
capable of collecting morphological and molecular information about a sample simultaneously. The combined
instrument will be used to investigate remaining technical challenges to combine these imaging modalities, such
as the laser power levels needed to achieve a Raman signal above the noise level without damaging the sample.
We describe a novel instrument that combines adaptive optics - Fourier-domain optical coherence tomography (AO-OCT) with an adaptive optics scanning laser ophthalmoscope (AO-SLO). Both systems share a common AO sub-system and vertical scanner to permit simultaneous acquisition of retinal images from both OCT and SLO. One of the benefits of combining OCT with SLO includes automatic co-registration between the two imaging modalities and potential for correcting lateral and transversal eye motion resulting in motion artifact-free volumetric retinal imaging. Results of using this system for eye model imaging are presented. Feasibility for clinical application is briefly discussed as well as potential further improvements of the current system.
Recent developments in adaptive optics - optical coherence tomography (AO-OCT) allow for ultra-high isotropic resolution imaging of the
in-vivo retina, offering unprecedented insight into its volumetric microscopic and cellular structures. In addition to this promising achievement, the clinical impact and application of this technology still needs to be explored. This includes assessment of limitations and challenges for existing as well as future AO-OCT systems,
especially in the context of potential transfer of this technology from an optical bench to a portable imaging system. To
address these issues we will describe our current AO-UHR-OCT focusing on its sub-components, as well as application for clinical imaging. Additionally, we describe some directions for future development of our AO-OCT instrument that would improve its clinical utility including: new compact AO-OCT design, new improved AO sub-system (extreme AO), and new generations of Fourier-domain-OCT.
We present testbed results of the Apodized Pupil Lyot Coronagraph (APLC) at the Laboratory for Adaptive Optics (LAO). This coronagraph is being built for the Gemini Planet Imager (GPI). The apodizer component is manufactured with a halftone technique using black chrome microdots on glass. Testing this APLC (like any other coronagraph) requires extremely good wavefront correction, which is obtained to the 1nm RMS level on the Extreme Adaptive Optics (ExAO) visible testbed of the Laboratory Adaptive optics (LAO) at the University of Santa Cruz.
With this testbed, we investigated the performance of the APLC coronagraph and more particularly the effect of the apodizer profile accuracy on the contrast.
We obtained the first image of a dark zone in a coronagraphic image with a MEMS deformable mirror. Finally, we compare the resulting contrast to predictions made with a wavefront propagation model of the testbed to understand the effects of phase and amplitude errors on the final contrast.
High-contrast adaptive optics systems, such as those needed to image extrasolar planets, are known to require
excellent wavefront control and diffraction suppression. The Laboratory for Adaptive Optics at UC Santa Cruz is
investigating limits to high-contrast imaging in support of the Gemini Planet Imager. Previous contrast measurements
were made with a simple single-opening prolate spheroid shaped pupil that produced a limited region of
high-contrast, particularly when wavefront errors were corrected with the 1024-actuator Boston Micromachines
MEMS deformable mirror currently in use on the testbed. A more sophisticated shaped pupil is now being used
that has a much larger region of interest facilitating a better understanding of high-contrast measurements. In
particular we examine the effect of heat sources in the testbed on PSF stability. We find that rms image motion
scales as 0.02 &lgr;/D per watt when the heat source is near the pupil plane. As a result heat sources of greater
than 5 watts should be avoided near pupil planes for GPI. The safest place to introduce heat is near a focal
plane. Heat also can effect the standard deviation of the high-contrast region but in the final instrument other
sources of error should be more significant.
Ultra-high isotropic resolution imaging of retinal structures was made possible with an adaptive optics system using dual deformable mirrors and a Fourier-domain optical coherence tomography (Fd-OCT) system with correction for longitudinal chromatic aberration. This system was used to image microscopic retinal structures of healthy as well as diseased retinas in vivo. The improved resolution and contrast enhanced visualization of morphological structures in the retina can be clearly seen. The benefits of this instrument are apparent from comparison of new images with those acquired using a previous generation AO-OCT instrument. Big change in the appearance of speckle field (reduction in speckle size) can be observed as well. Additionally, further improvements in volumetric data acquisition and image representation will be discussed. This includes creation of large Field of View (FOV) AO-OCT volume from multiple sub-volumes and its visualization. Also techniques and results of reducing speckle contrast by averaging multiple B-scans will be presented.
Micro-electrical-mechanical-systems (MEMS) deformable mirrors (DMs) are under study at the Laboratory for
Adaptive Optics for inclusion in possible future adaptive optics systems, including open loop or extreme adaptive
optics (ExAO) systems. MEMS DMs have several advantages in these areas because of low (to zero) hysterisis
and high actuator counts. In this paper, we present work in the area of high-contrast adaptive optics systems,
such as those needed to image extrasolar planets. These are known to require excellent wavefront control and
diffraction suppression. On the ExAO testbed we have already demonstrated wavefront control of better than
1 nm rms within controllable spatial frequencies, however, corresponding contrast measurements are limited by
amplitude variations, including variations introduced by the MEMS. Results from experimental measurements
and wave optic simulations on the ExAO testbed will be presented. In particular the effect of small scale
MEMS structures on amplitude variations and ultimately high-contrast far field measurements will be examined.
Experimental results include interferometer measurements of phase and amplitude using the phase shifting
diffraction interferometer, direct imaging of the pupil, and far-field imaging.
We describe a compact MEMS-based adaptive optics (AO) optical coherence tomography (OCT)
system with improved AO performance and ease of clinical use. A typical AO system consists of a
Shack-Hartmann wavefront sensor and a deformable mirror that measures and corrects the ocular
and system aberrations. Because of limitations on current deformable mirror technologies, the
amount of real-time ocular-aberration compensation is restricted and small in previous AO-OCT
instruments. In this instrument, we incorporate an optical apparatus to correct the spectacle
aberrations of the patients such as myopia, hyperopia and astigmatism. This eliminates the tedious
process of using trial lenses in clinical imaging. Different amount of spectacle aberration
compensation was achieved by motorized stages and automated with the AO computer for ease of
clinical use. In addition, the compact AO-OCT was optimized to have minimum system aberrations
to reduce AO registration errors and improve AO performance.
Adaptive optics (AO) and optical coherence tomography (OCT) are powerful imaging modalities that, when
combined, can provide high-resolution, 3-D images of the retina. The AO-OCT system at UC Davis has been
under development for 2 years and has demonstrated the utility of this technology for microscopic, volumetric, in
vivo retinal imaging. The current system uses a bimorph deformable mirror (DM) made by AOptix Technologies,
Inc. for low-order, high-stroke correction and a 140-actuator mirco-electrical-mechanical-system (MEMS) DM
made by Boston Micromachines Corporation for high-order correction. We present our on-going characterization
of AO system performance. The AO-OCT system typically has residual wavefront error of 100 nm rms. The
correctable error in the system is dominated by low-order error that we believe is introduced by aliasing in the
control loop. Careful characterization of the AO system will lead to improved performance and inform the design
of future systems.
High-contrast adaptive optics systems, such as those needed to image extrasolar planets, are known to require
excellent wavefront control and diffraction suppression. At the Laboratory for Adaptive Optics on the Extreme
Adaptive Optics testbed, we have already demonstrated wavefront control of better than 1 nm rms within controllable
spatial frequencies. Corresponding contrast measurements, however, are limited by amplitude variations,
including those introduced by the micro-electrical-mechanical-systems (MEMS) deformable mirror. Results from
experimental measurements and wave optic simulations of amplitude variations on the ExAO testbed are presented.
We find systematic intensity variations of about 2% rms, and intensity variations with the MEMS to
be 6%. Some errors are introduced by phase and amplitude mixing because the MEMS is not conjugate to
the pupil, but independent measurements of MEMS reflectivity suggest that some error is introduced by small
non-uniformities in the reflectivity.
Ultrahigh axial resolution in adaptive optics - optical coherence tomography (AO-OCT) is fundamentally limited by the
intrinsic chromatic aberrations of the human eye. Variation in refractive index of the ocular media with wavelength
causes the spectral content of broadband light sources to focus at different depths in the retina for light entering the eye
and at the imaging detector for light exiting. This effect has not been previously reported for ultrahigh-resolution OCT
(without AO) likely because the effect is masked by the relatively long depth of focus dictated by the small pupils used
in these systems. With AO, the pupil size is much larger and depth of focus substantially narrower. As such the
chromatic aberrations of the eye can counteract the lateral resolution benefit of AO when used with broadband light
sources. To more fully tap the potential of AO-OCT, compensation of the eye's chromatic and monochromatic
aberrations must occur concurrently. One solution is to insert an achromatizing lens in front of the eye whose chromatic
aberrations are equal but opposite in sign to that of the eye. In this paper we evaluate the efficacy of a novel design that
uses a custom achromatizing lens placed near the fiber collimating optic. AO-OCT images are acquired on several
subjects with and without the achromatizing lens and in combination with two light sources of different spectral width.
The combination of the achromatizing lens and broadband light source yielded the sharpest images of the retina and the
smallest speckle.
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.
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 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.
"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. A simple optical design allows us to minimize wavefront error and maximize the experimentally achievable contrast before progressing to a more complex set-up. A phase shifting diffraction interferometer is used to measure wavefront errors with sub-nm precision and accuracy. We have demonstrated RMS wavefront errors of <1.3 nm and a contrast of >10-7 over a substantial region using a shaped pupil. Current work includes the installation and characterization of a 1024-actuator Micro-Electro-Mechanical-Systems (MEMS) deformable mirror, manufactured by Boston Micro-Machines, which will be used for wavefront control. In our initial experiments we can flatten the deformable mirror to 1.8-nm RMS wavefront error within a control radius of 5-13 cycles per aperture. Ultimately this testbed will be used to test all aspects of the system architecture for an extrasolar planet-finding AO system.
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.
Ground based adaptive optics is a potentially powerful technique for direct imaging detection of extrasolar planets. Turbulence in the Earth's atmosphere imposes some fundamental limits, but the large size of ground-based telescopes compared to spacecraft can work to mitigate this. We are carrying out a design study for a dedicated ultra-high-contrast system, the eXtreme Adaptive Optics Planet Imager (XAOPI), which could be deployed on an 8-10m telescope in 2007. With a 4096-actuator MEMS deformable mirror it should achieve Strehl >0.9 in the near-IR. Using an innovative spatially filtered wavefront sensor, the system will be optimized to control scattered light over a large radius and suppress artifacts caused by static errors. We predict that it will achieve contrast levels of 107-108 at angular separations of 0.2-0.8" around a large sample of stars (R<7-10), sufficient to detect Jupiter-like planets through their near-IR emission over a wide range of ages and masses. We are constructing a high-contrast AO testbed to verify key concepts of our system, and present preliminary results here, showing an RMS wavefront error of <1.3 nm with a flat mirror.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.