The small correction volume for conventional wavefront shaping methods limits their application in biological imaging through scattering media. In this paper, we take advantage of conjugate adaptive optics (CAO) and remote focusing (CAORF) to achieve three-dimensional (3D) scanning through a scattering layer with a single correction. Our results show that the proposed system can provide 10 times wider axial field of view compared with a conventional conjugate AO system when 16,384 segments are used on a spatial light modulator. We demonstrate two-photon imaging with CAORF through mouse skull. The fluorescent microspheres embedded under the scattering layers can be clearly observed after applying the correction.
Marc Reinig, Samuel Novak, Xiaodong Tao, Laurent Bentolila, Dustin Roberts, Allan MacKenzie-Graham, Sirie Godshalk, Mary Raven, David Knowles, Joel Kubby
Our ability to see fine detail at depth in tissues is limited by scattering and other refractive characteristics of the tissue. For fixed tissue, we can limit scattering with a variety of clearing protocols. This allows us to see deeper but not necessarily clearer. Refractive aberrations caused by the bulk index of refraction of the tissue and its variations continue to limit our ability to see fine detail. Refractive aberrations are made up of spherical and other Zernike modes, which can be significant at depth. Spherical aberration that is common across the imaging field can be corrected using an objective correcting collar, although this can require manual intervention. Other aberrations may vary across the imaging field and can only be effectively corrected using adaptive optics. Adaptive optics can also correct other aberrations simultaneously with the spherical aberration, eliminating manual intervention and speeding imaging. We use an adaptive optics two-photon microscope to examine the impact of the spherical and higher order aberrations on imaging and contrast the effect of compensating only for spherical aberration against compensating for the first 22 Zernike aberrations in two tissue types. Increase in image intensity by 1.6× and reduction of root mean square error by 3× are demonstrated.
In this paper, we demonstrate a fast binary intensity modulation based on the measurement of the binary TM. For each correction, the binary TM was calculated based on measurements of the intensity change at the target with a series of input masks. After preloading the measurement masks, the DMD can run at full speed during measurement. The system allows dynamic focusing at 12.5 Hz with 1024 input modes, and more than 60 times intensity enhancement. We demonstrate focusing light through a highly dynamic scattering sample, a live drosophila embryo.
Optical sectioning of biological tissues has become the method of choice for three-dimensional histological analyses.
This is particularly important in the brain were neurons can extend processes over large distances and often whole brain
tracing of neuronal processes is desirable. To allow deeper optical penetration, which in fixed tissue is limited by
scattering and refractive index mismatching, tissue-clearing procedures such as CLARITY have been developed.
CLARITY processed brains have a nearly uniform refractive index and three-dimensional reconstructions at cellular
resolution have been published. However, when imaging in deep layers at submicron resolution some limitations caused
by residual refractive index mismatching become apparent, as the resulting wavefront aberrations distort the microscopic
image. The wavefront can be corrected with adaptive optics. Here, we investigate the wavefront aberrations at different
depths in CLARITY processed mouse brains and demonstrate the potential of adaptive optics to enable higher resolution
and a better signal-to-noise ratio. Our adaptive optics system achieves high-speed measurement and correction of the
wavefront with an open-loop control using a wave front sensor and a deformable mirror. Using adaptive optics enhanced
microscopy, we demonstrate improved image quality wavefront, point spread function, and signal to noise in the cortex
of YFP-H mice.
The design of an Adaptive Optics (AO) Structured Illumination (SI) microscope is presented. Two key technologies are
combined to provide effective super-resolution at significant depths in tissue. AO is used to measure and compensate for
optical aberrations in both the system and the tissue by measuring the optical path differences in the wavefront.
Uncorrected, these aberrations significantly reduce imaging resolution, particularly as we view deeper into tissue. SI
allows us to reconstruct an image with resolution beyond the Rayleigh limit of the optics by aliasing high spatial
frequencies, outside the limit of the optics, to lower frequencies within the system pass band. The aliasing is
accomplished by spatially modulating the illumination at a frequency near the cutoff frequency of the system. These
aliased frequencies are superimposed on the lower spatial frequencies of the object in our image. Using multiple images
and an inverse algorithm, we separate the aliased and normal frequencies, restore them to their original frequency
positions, and recreate the original spectrum of the object. This allows us to recreate a super-resolution image of the
object. A problem arises with thick aberrating tissue. Tissue aberrations, including sphere, increase with depth into the
tissue and reduce the high spatial frequency response of a system. This degrades the ability of SI to reconstruct at superresolution
and limits its use to relatively shallow depths. However, adding AO to the system compensates for these
aberrations allowing SI to work at maximum efficiency even deep within aberrating tissue.
We evaluate the performance of a woofer-tweeter controller architecture for the new 3-meter Shane Telescope (Lick Observatory) laser guidestar adaptive optics (AO) system. Low order, high stroke phase correction is performed using the normal modal basis set of the Alpao woofer deformable mirror (DM). Since the woofer and tweeter DMs share the same wavefront sensor, the projected woofer phase correction is offloaded from the high-order, low stroke phase aberrations corrected by the tweeter DM. This ensures the deformable mirrors complementarily correct the input phase disturbance and minimizes likelihood of the tweeter actuators saturating. Preliminary analysis of on-sky closed-loop deformable mirror telemetry data from currently operating AO systems at Mt. Hamilton, as well as statistically accurate Kolmogorov phase screens, indicate that correction of up to 34 woofer modes results in all tweeter actuators remaining within their stroke limit.
The Lick Observatory 3-meter telescope has a history of serving as a testbed for innovative adaptive optics techniques.
In 1996, it became one of the first astronomical observatories to employ laser guide star (LGS) adaptive optics as a
facility instrument available to the astronomy community. Work on a second-generation LGS adaptive optics system,
ShaneAO, is well underway, with plans to deploy on telescope in 2013. In this paper we discuss key design features and
implementation plans for the ShaneAO adaptive optics system. Once again, the Shane 3-m will host a number of new
techniques and technologies vital to the development of future adaptive optics systems on larger telescopes. Included is a
woofer-tweeter based wavefront correction system incorporating a voice-coil actuated, low spatial and temporal
bandwidth, high stroke deformable mirror in conjunction with a high order, high bandwidth MEMs deformable mirror.
The existing dye laser, in operation since 1996, will be replaced with a fiber laser recently developed at Lawrence
Livermore National Laboratories. The system will also incorporate a high-sensitivity, high bandwidth wavefront sensor
camera. Enhanced IR performance will be achieved by replacing the existing PICNIC infrared array with an Hawaii
2RG. The updated ShaneAO system will provide opportunities to test predictive control algorithms for adaptive optics.
Capabilities for astronomical spectroscopy, polarimetry, and visible-light adaptive optical astronomy will be supported.
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.
We demonstrated the used of an adaptive optic system in biological imaging to improve the imaging characteristics of a
wide field microscope. A crimson red fluorescent bead emitting light at 650 nm was used together with a Shack-Hartmann wavefront sensor and deformable mirror to compensate for the aberrations introduce by a Drosophila embryo.
The measurement and correction at one wavelength improves the resolving power at a different wavelength, enabling the
structure of the sample to be resolved (510 nm). The use of the crimson beads allow for less photobleaching to be done
to the science object of the embryo, in this case our GFP model (green fluorescent beads), and allows for the science
object and wavefront reference to be spectrally separated. The spectral separation allows for single points sources to be
used for wavefront measurements, which is a necessary condition for the Shack-Hartmann Wavefront sensor operation.
We report on the preliminary design of W.M. Keck Observatory's (WMKO's) next-generation adaptive optics (NGAO)
facility. This facility is designed to address key science questions including understanding the formation and evolution
of today's galaxies, measuring dark matter in our galaxy and beyond, testing the theory of general relativity in the
Galactic Center, understanding the formation of planetary systems around nearby stars, and exploring the origins of our
own solar system. The requirements derived from these science questions have resulted in NGAO being designed to
have near diffraction-limited performance in the near-IR (K-Strehl ~ 80%) over narrow fields (< 30" diameter) with
modest correction down to ~ 700 nm, high sky coverage, improved sensitivity and contrast and improved photometric
and astrometric accuracy. The resultant key design features include multi-laser tomography to measure the wavefront
and correct for the cone effect, open loop AO-corrected near-IR
tip-tilt sensors with MEMS deformable mirrors (DMs)
for high sky coverage, a high order MEMS DM for the correction of atmospheric and telescope static errors to support
high Strehls and high contrast companion sensitivity, point spread function (PSF) calibration to benefit quantitative
astronomy, a cooled science path to reduce thermal background, and a high-efficiency science instrument providing
imaging and integral field spectroscopy.
KEYWORDS: Tomography, Real-time computing, Cameras, Adaptive optics, Control systems, Stars, Wavefronts, Infrared cameras, Field programmable gate arrays, Process control
The next generation adaptive optics systems for large telescopes will be complex systems far larger, more complex, and
with higher performance than any currently installed. This requires adopting new algorithms, technologies, and
architectures. The Keck next generation adaptive optics (NGAO) system requires real-time wavefront reconstruction
and tomography given input from 7 laser and 3 natural guide stars. Requirements include 2 KHz atmospheric sampling,
tomographic atmosphere estimation, and control for 5 deformable mirrors. We take advantage of the algorithms'
massive parallelism and realize it on a massive array of FPGAs, GPUs, and multi-core CPUs. This paper presents the
current design and analysis of the NGAO system.
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.
The Keck Next Generation Adaptive Optics (KNGAO) system promises to yield high-Strehl observations over a
wide range of science wavelengths from the optical through the infrared. We describe the algorithms proposed for a
Real-Time Controller (RTC) implemented in a massive parallel processor environment. These algorithms take
advantage of the Fourier domain to speed up processing and ensure minimum variance control that incorporates
prior as well as current data. We present the unique approach to the design that enables such a complex tomography
processor to scale more favorably with telescope aperture size than the more traditional RTC approaches.
W. M. Keck Observatory (WMKO) is currently engaged in the design of a powerful new Adaptive Optics (AO) science
capability providing precision correction in the near-IR, good correction in the visible, and faint object multiplexed
integral field spectroscopy. Improved sensitivity will result from significantly higher Strehl ratios over narrow fields (<
30" diameter) and from lower backgrounds. Quantitative astronomy will benefit from improved PSF stability and
knowledge. Strehl ratios of 15 to 25% are expected at wavelengths as short as 750 nm. A multi-object AO approach
will be taken for the correction of multiple science targets over modest fields of regard (< 2' diameter) and to achieve
high sky coverage using AO compensated near-IR tip/tilt sensing. In this paper we present the conceptual design for this
system including discussion of the requirements, system architecture, key design features, performance predictions and
implementation plans.
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.
We investigate the non-modulating pyramid wave-front sensor's (P-WFS) implementation in the context of Lick
Observatory's Villages visible light AO system on the Nickel 1-meter telescope. A complete adaptive optics correction,
using a non-modulated P-WFS in slope sensing mode as a boot-strap to a regime in which the P-WFS can act as a direct
phase sensor is explored. An iterative approach to reconstructing the wave-front phase, given the pyramid wave-front
sensor's non-linear signal, is developed. Using Monte Carlo simulations, the iterative reconstruction method's photon
noise propagation behavior is compared to both the pyramid sensor used in slope-sensing mode, and the traditional
Shack Hartmann sensor's theoretical performance limits. We determine that bootstrapping using the P-WFS as a slope
sensor does not offer enough correction to bring the phase residuals into a regime in which the iterative algorithm can
provide much improvement in phase measurement. It is found that both the iterative phase reconstructor and the slope
reconstruction methods offer an advantage in noise propagation over Shack Hartmann sensors.
The Next Generation Adaptive Optics (NGAO) system will represent a considerable advancement for high resolution
astronomical imaging and spectroscopy at the W. M. Keck Observatory. The AO system will incorporate multiple laser
guidestar tomography to increase the corrected field of view and remove the cone effect inherent to single laser guide
star systems. The improvement will permit higher Strehl correction in the near-infrared and diffraction-limited correction
down to R band. A high actuator count micro-electromechanical system (MEMS) deformable mirror will provide the
on-axis wavefront correction to a number of instrument stations and additional MEMS devices will feed multiple
channels of a deployable integral-field spectrograph. In this paper we present the status of the AO system design and
describe its various operating modes.
We 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.
Performance of adaptive optics (AO) systems is limited by the tradeoff between photon noise at the wavefront sensor and
temporal error from the duty cycle of the controller. Optimal control studies have shown that this temporal error can be
reduced by predicting the turbulence evolution during the control cycle. We formulate a wind model that divides the
wind into two components: a quasi-static layer and a wind-driven frozen-flow layer. Using this internal wind model, we
design a computationally efficient controller that is able to estimate and predict the dynamics of a single windblown
layer and simulate this controller using on-sky data from the Palomar Adaptive Optics system.
We also present results from a laboratory implementation of multi-conjugate AO (MCAO) with multi-layer wind
estimation in conjunction with tomographic reconstruction. The tomography engine breaks the atmosphere into discrete
layers, each with its own wind estimator. The resulting MCAO control algorithm is able to track and predict the motion
of multiple wind layers with wind estimates that update at every controller cycle.
Once the wind velocities of each layer are known, the deformable mirror update speed is no longer limited by the
wavefront sensor exposure time so it is possible to send multiple correction updates to the deformable mirror each
control cycle in order to dynamically track wind layers across the telescope aperture. The result is better dynamics in the
feedback control system that enables higher closed-loop bandwidth for a given wavefront sensor frame rate.
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.
We present first results from the Multi-Conjugate and Multi-Object Adaptive Optics (MCAO and MOAO) testbed, at the UCO/Lick Laboratory for Adaptive Optics (LAO) facility at U.C. Santa Cruz. This testbed is constructed to simulate a 30-m telescope executing MCAO and/or open loop MOAO atmospheric compensation and imaging over 5 arcminutes. It is capable of performing Shack-Hartmann wavefront sensing on up to 8 natural or laser guide stars and 2-3 additional tip/tilt stars. In this paper, we demonstrate improved on-axis correction relative to ground layer adaptive optics (~ 15% Strehl relative to ~ 12%) with a simulated 28-m aperture at a D/r0 corresponding to a science wavelength of 2.6 microns using three laser guide stars on a simulated 41 arcsec radius with a central science object and one deformable mirror at the ground layer.
An adaptive optics system using multiple deformable mirrors and an array of guidestars can correct over a wider field of view than traditional single DM systems and can also eliminate the cone-effect error due to the finite altitude of laser guidestars. In large telescope systems, such as the envisioned 30-meter telescope, or TMT, the extraordinarily large amount of computation needed to implement multi-conjugate adaptive optics at atmospheric turnover rates is prohibitive for ordinary CPUs, even when another ten years of computer development is taken into account. We present here a novel approach, implementing a fast iterative version of the key inverse tomography calculations in an array of parallel computing elements. Our initial laboratory experiments using field-programmable gate arrays (FPGAs) are promising in terms of speed and convergence rates. In this paper we present the theory and results from simulations and experiments.
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