Showing papers on "Adaptive optics published in 2006"
TL;DR: In this paper, the authors proposed an acquisition strategy and reduction pipeline for speckle attenuation and high contrast imaging is demonstrated to significantly get better detection limits with longer integration times at all angular separations.
Abstract: Angular differential imaging is a high-contrast imaging technique that reduces speckle noise from quasi-static optical aberrations and facilitates the detection of faint nearby companions. A sequence of images is acquired with an altitude/azimuth telescope, the instrument rotator being turned off. This keeps the instrument and telescope optics aligned, stabilizes the instrumental PSF and allows the field of view to rotate with respect to the instrument. For each image, a reference PSF obtained from other images of the sequence is subtracted. All residual images are then rotated to align the field and are median combined. Observed performances are reported for Gemini Altair/NIRI data. Inside the speckle dominated region of the PSF, it is shown that quasi-static PSF noise can be reduced by a factor {approx}5 for each image subtraction. The combination of all residuals then provides an additional gain of the order of the square root of the total number of images acquired. To our knowledge, this is the first time an acquisition strategy and reduction pipeline designed for speckle attenuation and high contrast imaging is demonstrated to significantly get better detection limits with longer integration times at all angular separations. A PSF noise attenuation of 100 was achieved from 2-hourmore » long sequences of images of Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than 7''. This technique can be used with currently available instruments to search for {approx} 1 M{sub Jup} exoplanets with orbits of radii between 50 and 300 AU around nearby young stars. The possibility of combining the technique with other high-contrast imaging methods is briefly discussed.« less
1,182 citations
TL;DR: It is demonstrated here that resolution and signal size in two-photon microcopy can be substantially improved, even in living biological specimens, by adaptive wavefront correction based on sensing the wavefront of coherence-gated backscattered light and wavefront control by a deformable mirror.
Abstract: The image quality of a two-photon microscope is often degraded by wavefront aberrations induced by the specimen. We demonstrate here that resolution and signal size in two-photon microcopy can be substantially improved, even in living biological specimens, by adaptive wavefront correction based on sensing the wavefront of coherence-gated backscattered light (coherence-gated wavefront sensing, CGWS) and wavefront control by a deformable mirror. A nearly diffraction-limited focus can be restored even for strong aberrations. CGWS-based wavefront correction should be applicable to samples with a wide range of scattering properties and it should be possible to perform real-time pixel-by-pixel correction even at fast scan speeds.
354 citations
TL;DR: The first 8-10 m class telescope equipped with a laser guide star adaptive optics (LGS AO) system is the Keck II Telescope as mentioned in this paper, which produces K-band Strehl ratios between 30% and 40% using bright tip-tilt guide stars.
Abstract: The Keck II Telescope is the first 8-10 m class telescope equipped with a laser guide star adaptive optics (LGS AO) system. Under normal seeing conditions, the LGS AO system produces K-band Strehl ratios between 30% and 40% using bright tip-tilt guide stars, and it works well with tip-tilt guide stars as faint as , with partial correction for stars up to a magnitude fainter. This paper presents the algorithms implemented m p 18 R in the LGS AO system, as well as experimental performance results. A detailed error budget shows excellent agreement between the measured and expected image quality for both bright and faint guide stars.
277 citations
TL;DR: In this paper, Malbet et al. developed two analytical methods for wave front sensing and control that aim at creating "dark holes", i.e., areas of the image plane cleared of speckles, assuming an ideal coronagraph and small aberrations.
Abstract: High-contrast imaging from space must overcome two major noise sources to successfully detect a terrestrial planet angularly close to its parent star: photon noise from diffracted starlight and speckle noise from starlight scattered by instrumentally generated wave front perturbation. Coronagraphs tackle only the photon noise contribution by reducing diffracted starlight at the location of a planet. Speckle noise should be addressed with adaptive optics systems. Following the tracks of Malbet, Yu, and Shao, we develop in this paper two analytical methods for wave front sensing and control that aims at creating "dark holes," i.e., areas of the image plane cleared of speckles, assuming an ideal coronagraph and small aberrations. The first method, "speckle field nulling," is a fast FFT-based algorithm that requires the deformable-mirror influence functions to have identical shapes. The second method, "speckle energy minimization," is more general and provides the optimal deformable mirror shape via matrix inversion. With an N × N deformable mirror, the size of the matrix to be inverted is either N2 × N2 in the general case or only N × N if the influence functions can be written as the tensor product of two one-dimensional functions. Moreover, speckle energy minimization makes it possible to trade off some of the dark hole area against an improved contrast. For both methods, complex wave front aberrations (amplitude and phase) are measured using just three images taken with the science camera (no dedicated wave front sensing channel is used); therefore, there are no noncommon path errors. We assess the theoretical performance of both methods with numerical simulations including realistic speckle noise and experimental influence functions. We find that these speckle-nulling techniques should be able to improve the contrast by several orders of magnitude.
274 citations
TL;DR: The first observations of the three-dimensional morphology of cone photoreceptors in the living human retina are reported, with regular distribution of bright spots observed within C-scans at the inner segment / outer segment (IS/OS) junctions and at the posterior tips of the OS were found to be highly correlated with one another and with the expected cone spacing.
Abstract: We report the first observations of the three-dimensional morphology of cone photoreceptors in the living human retina. Images were acquired with a high-speed adaptive optics (AO) spectral-domain optical coherence tomography (SD-OCT) camera. The AO system consisted of a Shack-Hartmann wavefront sensor and bimorph mirror (AOptix) that measured and corrected the ocular and system aberrations at a closed-loop rate of 12 Hz. The bimorph mirror was positioned between the XY mechanical scanners and the subject's eye. The SD-OCT system consisted of a superluminescent diode and a 512 pixel line scan charge-coupled device (CCD) that acquired 75,000 A-scans/s. This rate is more than two times faster than that previously reported. Retinal motion artifacts were minimized by quickly acquiring small volume images of the retina with and without AO compensation. Camera sensitivity was sufficient to detect reflections from all major retinal layers. The regular distribution of bright spots observed within C-scans at the inner segment / outer segment (IS/OS) junctions and at the posterior tips of the OS were found to be highly correlated with one another and with the expected cone spacing. No correlation was found between the posterior tips of the OS and the other retinal layers examined, including the retinal pigment epithelium.
253 citations
TL;DR: A feasibility study is proposed for an extreme AO system in the frame of the SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument, which is currently under design and should equip one of the four VLT 8-m telescopes in 2010.
Abstract: The detection of extrasolar planets implies an extremely high-contrast, long-exposure imaging capability at near infrared and probably visible wavelengths We present here the core of any Planet Finder instrument, that is, the extreme adaptive optics (XAO) subsystem The level of AO correction directly impacts the exposure time required for planet detection In addition, the capacity of the AO system to calibrate all the instrument static defects ultimately limits detectivity Hence, the extreme AO system has to adjust for the perturbations induced by the atmospheric turbulence, as well as for the internal aberrations of the instrument itself We propose a feasibility study for an extreme AO system in the frame of the SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument, which is currently under design and should equip one of the four VLT 8-m telescopes in 2010
216 citations
TL;DR: The OSIRIS integral field spectrograph (OSIRIS) as mentioned in this paper was designed to sample a rectangular field of view at close to the Keck diffraction limit by packing the spectra close together and using the Rockwell Hawaii-2 detector.
Abstract: We present an overview of the OSIRIS integral field spectrograph which was recently commissioned on the Keck II Telescope. OSIRIS works with the Keck Adaptive Optics system and utilizes an infrared transmissive lenslet array to sample a rectangular field of view at close to the Keck diffraction limit. By packing the spectra close together (2 pixel rows per spectrum) and using the Rockwell Hawaii-2 detector (wavelengths between 1 and 2.5 microns), we achieve a relatively large field of view (up to 6."4) while maintaining full broad-band spectral coverage at a resolution of 3800. Among the challenges of the instrument are: a fully cryogenic design (approximately 250 kg are brought down to 55K); four spatial scales from 0."02 to 0."10; extremely low wavefront error (approximately 25 nm of non-common path error); large all aluminum optics for the spectrograph; extremely repeatable spectral formats; and a sophisticated data reduction pipeline. OSIRIS also serves as a starting point for our design of IRIS which is a planned integral field spectrograph for the Thirty Meter Telescope.
199 citations
TL;DR: A scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains and Adaptive optics correct the wavefront of each amplified beamlet.
Abstract: We demonstrate a scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains. A common master oscillator injects a sequence of multikilowatt Nd:YAG zigzag slab amplifiers. Adaptive optics correct the wavefront of each amplified beamlet. The beamlets are tiled side by side and actively phase locked to form a single output beam. The laser produces 19 kW with beam quality <2x diffraction limited. To the best of our knowledge, this is the brightest cw solid-state laser demonstrated to date.
187 citations
TL;DR: A model for the operation of certain adaptive optics systems is developed and a link with the geometrical problems of sphere packings and coverings is demonstrated and an efficient scheme using a direct maximisation calculation that permits the measurement of N Zernike modes with only N +1 intensity measurements is developed.
Abstract: Certain adaptive optics systems do not employ a wave front sensor but rather maximise a photodetector signal by appropriate control of an adaptive element. The maximisation procedure must be optimised if the system is to work efficiently. Such optimisation is often implemented empirically, but further insight can be obtained by using an appropriate mathematical model. In many practical systems aberrations can be accurately represented by a small number of modes of an orthogonal basis, such as the Zernike polynomials. By heuristic reasoning we develop a model for the operation of such systems and demonstrate a link with the geometrical problems of sphere packings and coverings. This approach aids the optimisation of control algorithms and is illustrated by application to direct search and hill climbing algorithms. We develop an efficient scheme using a direct maximisation calculation that permits the measurement of N Zernike modes with only N +1 intensity measurements.
180 citations
TL;DR: A significant increase in throughput allows for a confocal pinhole whose diameter is less than the Airy disc of the collection lens, thereby fully exploiting the axial resolution capabilities of the system.
Abstract: We have developed a compact, robust adaptive optics (AO) scanning laser ophthalmoscope using a microelectromechanical (MEMS) deformable mirror (DM). Facilitated with a Shack-Hartmann wavefront sensor, the MEMS-DM-based AO operates a closed-loop modal wave aberration correction for the human eye and reduces wave aberrations in most eyes to below 0.1 μm rms. Lateral resolution is enhanced, and images reveal a clear cone mosaic near the foveal center. The significant increase in throughput allows for a confocal pinhole whose diameter is less than the Airy disc of the collection lens, thereby fully exploiting the axial resolution capabilities of the system.
159 citations
TL;DR: Results from living eyes, including one exhibiting 4.66 D of myopia and a near pathologic cornea with notable high order aberrations, show a practically perfect aberration correction.
Abstract: A novel deformable mirror using 52 independent magnetic actuators (MIRAO 52, Imagine Eyes) is presented and characterized for ophthalmic applications. The capabilities of the device to reproduce different surfaces, in particular Zernike polynomials up to the fifth order, are investigated in detail. The study of the influence functions of the deformable mirror reveals a significant linear response with the applied voltage. The correcting device also presents a high fidelity in the generation of surfaces. The ranges of production of Zernike polynomials fully cover those typically found in the human eye, even for the cases of highly aberrated eyes. Data from keratoconic eyes are confronted with the obtained ranges, showing that the deformable mirror is able to compensate for these strong aberrations. Ocular aberration correction with polychromatic light, using a near Gaussian spectrum of 130 nm full width at half maximum centered at 800 nm, in five subjects is accomplished by simultaneously using the deformable mirror and an achromatizing lens, in order to compensate for the monochromatic and chromatic aberrations, respectively. Results from living eyes, including one exhibiting 4.66 D of myopia and a near pathologic cornea with notable high order aberrations, show a practically perfect aberration correction. Benefits and applications of simultaneous monochromatic and chromatic aberration correction are finally discussed in the context of retinal imaging and vision.
TL;DR: A novel computational technique known as the map-seeking circuit algorithm is applied to estimate the motion of the retina of eye from a sequence of frames of data from a scanning laser ophthalmoscope, and a scheme to dewarp and co-add frames of retinal image data, given the estimated motion.
Abstract: We apply a novel computational technique known as the map-seeking circuit algorithm to estimate the motion of the retina of eye from a sequence of frames of data from a scanning laser ophthalmoscope. We also present a scheme to dewarp and co-add frames of retinal image data, given the estimated motion. The motion estimation and dewarping techniques are applied to data collected from an adaptive optics scanning laser ophthalmoscopy.
TL;DR: A retinal imaging instrument that integrates adaptive optics, scanning laser ophthalmoscopy, and retinal tracking components was built and tested and has the potential to become an important tool to clinicians and researchers for vision studies and the early detection and treatment of retinal diseases.
Abstract: A retinal imaging instrument that integrates adaptive optics (AO), scanning laser ophthalmoscopy (SLO), and retinal tracking components was built and tested. The system uses a Hartmann-Shack wave-front sensor (HS-WS) and MEMS-based deformable mirror (DM) for AO-correction of high-resolution, confocal SLO images. The system includes a wide-field line-scanning laser ophthalmoscope for easy orientation of the high-magnification SLO raster. The AO system corrected ocular aberrations to <0.1 μm RMS wave-front error. An active retinal tracking with custom processing board sensed and corrected eye motion with a bandwidth exceeding 1 kHz. We demonstrate tracking accuracy down to 6 μm RMS for some subjects (typically performance: 10–15 μm RMS). The system has the potential to become an important tool to clinicians and researchers for vision studies and the early detection and treatment of retinal diseases.
Book•
18 Jul 2006
TL;DR: This work focuses on the development of Adaptive Optics in Vision Science and Ophthalmology and the application of these technologies in the field of Vision Correction.
Abstract: FOREWORD. ACKNOWLEDGMENTS. CONTRIBUTORS. PART ONE: INTRODUCTION. 1. Development of Adaptive Optics in Vision Science and Ophthalmology (David R. Williams and Jason Porter). 1.1 Brief History of Aberration Correction in the Human Eye. 1.2 Applications of Ocular Adaptive Optics. PART TWO: WAVEFRONT MEASUREMENT AND CORRECTION. 2. Aberration Structure of the Human Eye (Pablo Artal, Juan M. Bueno, Antonio Guirao, and Pedro M. Prieto). 2.1 Introduction. 2.2 Location of Monochromatic Aberrations Within the Eye. 2.3 Temporal Properties of Aberrations: Accommodation and Aging. 2.4 Chromatic Aberrations. 2.5 Off-Axis Aberrations. 2.6 Statistics of Aberrations in Normal Populations. 2.7 Effects of Polarization and Scatter. 3. Wavefront Sensing and Diagnostic Uses (Geunyoung Yoon). 3.1 Wavefront Sensors for the Eye. 3.2 Optimizing a Shack-Hartmann Wavefront Sensor. 3.3 Calibration of a Wavefront Sensor. 3.4 Summary. 4. Wavefront Correctors for Vision Science (Nathan Doble and Donald T. Miller). 4.1 Introduction. 4.2 Principal Components of an AO System. 4.3 Wavefront Correctors. 4.4 Wavefront Correctors Used in Vision Science. 4.5 Performance Predictions for Various Types of Wavefront Correctors. 4.6 Summary and Conclusion. 5. Control Algorithms (Li Chen). 5.1 Introduction. 5.2 Confi guration of Lenslets and Actuators. 5.3 Infl uence Function Measurement. 5.4 Spatial Control Command of the Wavefront Corrector. 5.5 Temporal Control Command of the Wavefront Corrector. 6. Adaptive Optics Software for Vision Research (Ben Singer). 6.1 Introduction. 6.3 Measuring Wavefront Slope. 6.4 Aberration Recovery. 6.5 Correcting Aberrations. 6.6 Application-Dependent Considerations. 6.7 Conclusion. 7. Adaptive Optics System Assembly and Integration (Brian J. Bauman and Stephen K. Eisenbies). 7.1 Introduction. 7.2 First-Order Optics of the AO System. 7.3 Optical Alignment. 7.4 AO System Integration. 8. System Performance Characterization (Marcos A. van Dam). 8.1 Introduction. 8.2 Strehl Ratio. 8.3 Calibration Error. 8.4 Fitting Error. 8.5 Measurement and Bandwidth Error. 8.6 Addition of Wavefront Error Terms. PART THREE: RETINAL IMAGING APPLICATIONS. 9. Fundamental Properties of the Retina (Ann E. Elsner). 9.1 Shape of the Retina. 9.2 Two Blood Supplies. 9.3 Layers of the Fundus. 9.4 Spectra. 9.5 Light Scattering. 9.6 Polarization. 9.7 Contrast from Directly Backscattered or Multiply Scattered Light. 9.8 Summary. 10. Strategies for High-Resolution Retinal Imaging (Austin Roorda, Donald T. Miller, and Julian Christou). 10.1 Introduction. 10.2 Conventional Imaging. 10.3 Scanning Laser Imaging. 10.4 OCT Ophthalmoscope. 10.5 Common Issues for all AO Imaging Systems. 10.6 Image Postprocessing. PART FOUR: VISION CORRECTION APPLICATIONS. 11. Customized Vision Correction Devices (Ian Cox). 11.1 Contact Lenses. 11.2 Intraocular Lenses. 12. Customized Corneal Ablation (Scott M. MacRae). 12.1 Introduction. 12.2 Basics of Laser Refractive Surgery. 12.3 Forms of Customization. 12.4 The Excimer Laser Treatment. 12.5 Biomechanics and Variable Ablation Rate. 12.6 Effect of the LASIK Flap. 12.7 Wavefront Technology and Higher Order Aberration Correction. 12.8 Clinical Results of Excimer Laser Ablation. 12.9 Summary. 13. From Wavefronts To Refractions (Larry N. Thibos). 13.1 Basic Terminology. 13.2 Goal of Refraction. 13.3 Methods for Estimating the Monochromatic Refraction from an Aberration Map. 13.4 Ocular Chromatic Aberration and the Polychromatic Refraction. 13.5 Experimental Evaluation of Proposed Refraction Methods. 14. Visual Psychophysics With Adaptive Optics (Joseph L. Hardy, Peter B. Delahunt, and John S. Werner). 14.1 Psychophysical Functions. 14.2 Psychophysical Methods. 14.3 Generating the Visual Stimulus. 14.4 Conclusions. PART FIVE: DESIGN EXAMPLES. 15. Rochester Adaptive Optics Ophthalmoscope (Heidi Hofer, Jason Porter, Geunyoung Yoon, Li Chen, Ben Singer, and David R. Williams) 15.1 Introduction. 15.2 Optical Layout. 15.3 Control Algorithm. 15.4 Wavefront Correction Performance. 15.5 Improvement in Retinal Image Quality. 15.6 Improvement in Visual Performance. 15.7 Current System Limitations. 15.8 Conclusion. 16. Design of an Adaptive Optics Scanning Laser Ophthalmoscope (Krishnakumar Venkateswaran, Fernando Romero-Borja, and Austin Roorda). 16.1 Introduction. 16.2 Light Delivery. 16.3 Raster Scanning. 16.4 Adaptive Optics in the SLO. 16.5 Optical Layout for the AOSLO. 16.6 Image Acquisition. 16.7 Software Interface for the AOSLO. 16.8 Calibration and Testing. 16.9 AO Performance Results. 16.10 Imaging Results. 16.11 Discussions on Improving Performance of the AOSLO. 17. Indiana University AO-OCT System (Yan Zhang, Jungtae Rha, Ravi S. Jonnal, and Donald T. Miller). 17.1 Introduction. 17.2 Description of the System. 17.3 Experimental Procedures. 17.4 AO Performance. 17.5 Example Results with AO Conventional Flood- Illuminated Imaging. 17.6 Example Results With AO Parallel SD-OCT Imaging. 17.7 Conclusion. 18. Design and Testing of A Liquid Crystal Adaptive OpticsPhoropter (Abdul Awwal and Scot Olivier). 18.1 Introduction. 18.2 Wavefront Sensor Selection. 18.3 Beacon Selection: Size and Power, SLD versus Laser Diode. 18.4 Wavefront Corrector Selection. 18.5 Wavefront Reconstruction and Control. 18.6 Software Interface. 18.7 AO Assembly, Integration, and Troubleshooting. 18.8 System Performance, Testing Procedures, and Calibration. 18.9 Results from Human Subjects. 18.10 Discussion. 18.11 Summary. APPENDIX A: OPTICAL SOCIETY OF AMERICA'S STANDARDS FOR REPORTING OPTICAL ABERRATIONS. GLOSSARY. SYMBOL TABLE. INDEX.
TL;DR: Inverse scattering theory for optical coherence tomography (OCT) is developed in this paper, and the results are used to produce algorithms to resolve three-dimensional object structure, taking into account the finite beam width, diffraction, and defocusing effects.
Abstract: Inverse scattering theory for optical coherence tomography (OCT) is developed. The results are used to produce algorithms to resolve three-dimensional object structure, taking into account the finite beam width, diffraction, and defocusing effects. The resolution normally achieved only in the focal plane of the OCT system is shown to be available for all illuminated depths in the object without moving the focal plane. Spatially invariant resolution is verified with numerical simulations and indicates an improvement of the high-resolution cross-sectional imaging capabilities of OCT.
TL;DR: In this paper, the authors determine the theoretical response of a SLODAR system based on a Shack-Hartmann WFS to a thin turbulent layer at a given altitude, and also as a function of the spatial power spectral index of the optical phase aberrations.
Abstract: Slope Detection and Ranging (SLODAR) is a technique for the measurement of the vertical profile of atmospheric optical turbulence strength. Its main applications are astronomical site characterization and real-time optimization of imaging with adaptive optical correction. The turbulence profile is recovered from the cross-covariance of the slope of the optical phase aberration for a double star source, measured at the telescope with a wavefront sensor (WFS). Here, we determine the theoretical response of a SLODAR system based on a Shack–Hartmann WFS to a thin turbulent layer at a given altitude, and also as a function of the spatial power spectral index of the optical phase aberrations. Recovery of the turbulence profile via fitting of these theoretical response functions is explored. The limiting resolution in altitude of the instrument and the statistical uncertainty of the measured profiles are discussed. We examine the measurement of the total integrated turbulence strength (the seeing) from the WFS data and, by subtraction, the fractional contribution from all turbulence above the maximum altitude for direct sensing of the instrument. We take into account the effects of noise in the measurement of wavefront slopes from centroids and the form of the spatial structure function of the atmospheric optical aberrations.
TL;DR: The correction of aberrations produced by the adaptive optics closed-loop system increased the signal-to-noise ratio in images obtained from volunteer eyes by up to 6 dB in the OCT channel and up to 9dB in the SLO channel.
Abstract: A novel combination of adaptive optics with a simultaneous en-face OCT/SLO system for high resolution imaging of the in-vivo human retina is presented. Pairs of retinal images are shown and performance of the system is evaluated with and without dynamic wavefront correction. The adaptive optics closed loop system operates at a frame rate of 9 Hz and incorporates a Shack-Hartmann wavefront sensor based on a highly sensitive Andor camera and a 37 actuator OKO membrane deformable mirror to correct for ocular aberrations. The system produces C-scan pairs of images at a frame rate of 2 Hz. The correction of aberrations produced by the adaptive optics closed-loop system increased the signal-to-noise ratio in images obtained from volunteer eyes by up to 6 dB in the OCT channel and up to 9 dB in the SLO channel. A slight improvement in the lateral resolution was also obtained, from 6.5 μm before to 5 μm after closing the adaptive optics loop.
TL;DR: A novel bench top flood-illumination camera is investigated that achieves significantly higher frame rates using strobing fiber-coupled superluminescent and laser diodes in conjunction with a scientific-grade CCD to evaluate the tradeoff between exposure duration and image blur associated with retina motion.
Abstract: Current adaptive optics flood-illumination retina cameras operate at low frame rates, acquiring retinal images below seven Hz, which restricts their research and clinical utility. Here we investigate a novel bench top flood-illumination camera that achieves significantly higher frame rates using strobing fiber-coupled superluminescent and laser diodes in conjunction with a scientific-grade CCD. Source strength was sufficient to obviate frame averaging, even for exposures as short as 1/3 msec. Continuous frame rates of 10, 30, and 60 Hz were achieved for imaging 1.8,0.8, and 0.4 deg retinal patches, respectively. Short-burst imaging up to 500 Hz was also achieved by temporarily storing sequences of images on the CCD. High frame rates, short exposure durations (1 msec), and correction of the most significant aberrations of the eye were found necessary for individuating retinal blood cells and directly measuring cellular flow in capillaries. Cone videos of dark adapted eyes showed a surprisingly rapid fluctuation (~1 Hz) in the reflectance of single cones. As further demonstration of the value of the camera, we evaluated the tradeoff between exposure duration and image blur associated with retina motion.
TL;DR: In this article, the authors report near-infrared (primarily H band) adaptive optics (AO) imaging with the Gemini-N and Subaru Tele-scopes, ofarepresentative sample of 32nearby(z 2L most are elliptical.
Abstract: We report near-infrared (primarily H band) adaptive optics (AO) imaging with the Gemini-N and Subaru Tele- scopes,ofarepresentativesampleof 32nearby(z 2Lmost are ellipticals. ''Disturbed'' hosts are found at all MH(host), while ''strongly disturbed'' hosts appear to favor the more luminous hosts. Hosts with prominent disks have less luminous QSOs, while the most luminous QSOs are almost exclusively in ellipticals or in mergers (which presumably shortly will be ellipticals). At z 0:15, the more luminous QSOs (MB 7L � ), most of which are ellipticals. Finally, we find a strong correlation between the ''infrared excess,'' LIR/LBB, of QSOs with host type and degree of disturbance. Disturbed and strongly disturbed hosts and hosts with dominant disks have LIR/LBB twice that of nondisturbed and elliptical hosts, respectively. QSOs with disturbed and strongly disturbed hosts are also found to have morphologies and mid/far-infrared colors that are similar to what is found for ''warm'' ultraluminous infrared galaxies, providing further evidence for a possible evo- lutionary connection between both classes of objects.
TL;DR: The OSIRIS integral field spectrograph (OSIRIS) as discussed by the authors uses an infrared transmissive lenslet array to sample a rectangular field of view at close to the Keck diffraction limit.
TL;DR: In this article, the authors proposed to use off-axis satellite PSFs produced by a periodic amplitude or phase mask conjugated to a pupil plane to correct the drift of the point spread function (PSF) with time.
Abstract: For ground-based adaptive optics point source imaging, differential atmospheric refraction and flexure introduce a small drift of the point spread function (PSF) with time, and seeing and sky transmission variations modify the PSF flux. These effects need to be corrected to properly combine the images and obtain optimal signal-to-noise ratios, accurate relative astrometry and photometry of detected companions as well as precise detection limits. Usually, one can easily correct for these effects by using the PSF core, but this is impossible when high dynamic range observing techniques are used, like coronagraphy with a non-transmissive occulting mask, or if the stellar PSF core is saturated. We present a new technique that can solve these issues by using off-axis satellite PSFs produced by a periodic amplitude or phase mask conjugated to a pupil plane. It will be shown that these satellite PSFs track precisely the PSF position, its Strehl ratio and its intensity and can thus be used to register and to flux normalize the PSF. This approach can be easily implemented in existing adaptive optics instruments and should be considered for future extreme adaptive optics coronagraph instruments and in high-contrast imaging space observatories.
TL;DR: This paper presents the foundations of a modeling method for the AO optical transfer function, based on an analytical description of the residual phase spatial power spectrum, in an IDL-based code, and comparison with end-to-end simulations demonstrates the validity of this approach.
Abstract: End-to-end simulation of adaptive optics (AO) systems allows high-fidelity modeling of system performance, but at the cost of long computation time. Analytical modeling, on the other hand, can provide much faster first-order performance estimates for a rapid exploration of the AO parameter space. In this paper, we present the foundations of a modeling method for the AO optical transfer function, based on an analytical description of the residual phase spatial power spectrum. The method has been implemented in an IDL-based code, PAOLA, and comparison with end-to-end simulations demonstrates the validity of the analytical approach.
TL;DR: A significant increase in throughput allows for a confocal pinhole whose diameter is less than the Airy disc of the collection lens, thereby fully exploiting the axial resolution capabilities of the system.
Abstract: We developed a clinically deployable adaptive optics (AO) scanning laser ophthalmoscope (AOSLO) using a micro-electro-mechanical (MEMS) deformable mirror and low coherent light sources. We investigated retina microstructure in retinal degeneration patients with high resolution.
TL;DR: A numerical wave optics approach for simulating a partial spatially coherent beam by application of a sequence of random phase screens to an initial beam field and the summation of the intensity results after propagation is presented.
Abstract: A numerical wave optics approach for simulating a partial spatially coherent beam is presented. The approach involves the application of a sequence of random phase screens to an initial beam field and the summation of the intensity results after propagation. The relationship between the screen parameters and the spatial coherence function for the beam is developed and the approach is verified by comparing results with analytic formulations for a Gaussian Schell-model beam. The approach can be used for modeling applications such as free space optical laser links that utilize partially coherent beams.
TL;DR: This work presents what is to their knowledge a first hardware realization of a simulated annealing algorithm in an adaptive optics system designed to image the retina of the human eye and finds that this optimization algorithm can be an alternative to the traditional Hartmann-Shack sensing.
Abstract: We present what is to our knowledge a first hardware realization of a simulated annealing algorithm in an adaptive optics system designed to image the retina of the human eye. The algorithm is applied to the retinal image itself without the need for wavefront sensors in the system. We find that this optimization algorithm can be an alternative to the traditional Hartmann-Shack sensing. We also compare the simulated annealing algorithm to the stochastic parallel gradient descent algorithm.
TL;DR: In this article, a fast readout mode was developed to take short exposures of stellar images corrected by adaptive optics at ground-based UCO/Lick Observatory, with integration times of 5 ms and a time between successive frames of 14.5 ms (λ = 2.2 μm).
Abstract: Imaging observations are generally affected by a fluctuating background of speckles, a particular problem when detecting faint stellar companions at small angular separations. These speckles can be created by both short-lived atmospheric aberrations and slowly changing distortions in the optical system. Over the course of a long-exposure image, the combination of many independent realizations of speckle patterns forms a halo in the point-spread function (PSF) of characteristic scale Δθ ~ λ/r0 (where r0 is the coherence length in the pupil). While adaptive optics can increase the achievable image contrast, speckle noise remains a major source of random error, which decreases the sensitivity of companion detection observations near the diffraction limit. Knowing the distribution of the speckle intensities at a given location in the image plane is therefore important for understanding the noise limits of companion detection. The speckle noise limit in a long-exposure image is characterized by the intensity variance and the speckle lifetime. In this paper we address the former quantity through the distribution function of speckle intensity. Previous theoretical work has predicted a form for this distribution function at a single location in the image plane. We developed a fast readout mode to take short exposures of stellar images corrected by adaptive optics at the ground-based UCO/Lick Observatory, with integration times of 5 ms and a time between successive frames of 14.5 ms (λ = 2.2 μm). These observations temporally oversample and spatially Nyquist sample the observed speckle patterns. We show, for various locations in the image plane, that the observed distribution of speckle intensities is consistent with the predicted form. In addition, we demonstrate a method by which Ic and Is can be mapped over the image plane. As the quantity Ic is proportional to the PSF of the telescope free of random atmospheric aberrations, this method can be used for PSF calibration and reconstruction.
TL;DR: In this paper, the authors analyzed the fundamental limitations for the detection of extraterrestrial planets with Extremely Large Telescopes and found that a coronagraphic device combined with a very high order wavefront correction system is not sufficient to achieve the 10 -10 contrast level needed to detect an Earth-like planet.
Abstract: We analyse the fundamental limitations for the detection of extraterrestrial planets with Extremely Large Telescopes. For this task, a coronagraphic device combined with a very high order wavefront correction system is required but is not sufficient to achieve the 10 -10 contrast level needed to detect an Earth-like planet. The stellar residuals left uncorrected by the wavefront correction system need to be calibrated and subtracted. We consider a general model including the dynamic phase aberrations downstream of the wavefront correction system, the static phase aberrations of the instrument and some differential aberrations provided by the calibration unit. A rather optimistic case of a filled circular pupil and of a perfect coronagraph is assumed. As a result of the analytical study, the limitation is found to mostly come from the static aberrations. We confirm this result using numerical simulations and evaluate the requirements in terms of phase aberrations to detect Earth-like planets with Extremely Large Telescopes.
TL;DR: In this article, the Fraunhofer approximation of Fourier optics is used to calibrate a periodic grid of wires with known width and spacing in a pupil plane in front of the occulting coronagraphic focal plane mask.
Abstract: We propose a solution to the problem of astrometric and photometric calibration of coronagraphic images with a simple optical device which, in theory, is easy to use. Our design uses the Fraunhofer approximation of Fourier optics. Placing a periodic grid of wires (we use a square grid) with known width and spacing in a pupil plane in front of the occulting coronagraphic focal plane mask produces fiducial images of the obscured star at known locations relative to the star. We also derive the intensity of these fiducial images in the coronagraphic image. These calibrator images can be used for precise relative astrometry, to establish companionship of other objects in the field of view through measurement of common proper motion or common parallax, to determine orbits, and to observe disk structure around the star quantitatively. The calibrator spots also have known brightness, selectable by the coronagraph designer, permitting accurate relative photometry in the coronagraphic image. This technique, which enables precision exoplanetary science, is relevant to future coronagraphic instruments, and is particularly useful for `extreme' adaptive optics and space-based coronagraphy.
TL;DR: In this paper, surface-micromachined deformable mirrors that exhibit greater than 10 /spl mu/m of stroke are presented, and a heat-treatment procedure is proposed for controlling mirror curvature to better than /spl lambda//10.
Abstract: Surface-micromachined deformable mirrors that exhibit greater than 10 /spl mu/m of stroke are presented. The segmented arrays described here consist of 61 and 85 hexagonal, piston/tip/tilt mirrors (three actuators each) with diameters of 500 and 430 /spl mu/m, respectively, and fill a 4 mm circular aperture. Devices were packaged in 208 and 256 pin-grid arrays and driven by a compact control board designed for turn-key operation. After metallization and packaging mirror bow is /spl sim/680 nm (/spl lambda//1), but a heat-treatment procedure is proposed for controlling mirror curvature to better than /spl lambda//10. An optical test bed was used to demonstrate basic beam splitting and open-loop aberration correction, the results of which are also presented.
TL;DR: Aberration correction and mirror control stability clearly increase when smaller beam steering amplitudes synonymous of higher wavefront sensing sensitivity are used and this result suggests that using pyramid wavefront sensors can improve the performance of adaptive-optics system for ophthalmic applications.
Abstract: A new adaptive optics system for the eye using a pyramid wavefront sensor interfaced in closed-loop with a piezoelectric deformable mirror is presented. Sensing parameters such as CCD integration time, pupil sampling and beam steering amplitude are tested on the bench and in vivo on several volunteers to optimize real-time optical correction. The system allows closed-loop operation at a frame rate of 55 Hz and reduces ocular aberration up to λ/5 residual RMS over a 6 mm pupil. Aberration correction and mirror control stability clearly increase when smaller beam steering amplitudes synonymous of higher wavefront sensing sensitivity are used. This result suggests that using pyramid wavefront sensors can improve the performance of adaptive-optics system for ophthalmic applications.