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High-resolution speckle imaging
摘要： One of the most exciting and challenging pursuits of 21st-century astrophysics is to identify an exoplanet—that is, a planet orbiting an alien sun—on which life may exist. Such a planet is likely to reside in the habitable zone of its sun, meaning that it can harbor liquid water on its surface. Many astrobiologists posit that a life-harboring planet must also be small, rocky, and similar in density to our own. One critical input to any future discovery will be a precise determination of the planet radius, a value that will probably be obtained with the help of high-resolution speckle imaging.
关键词： speckle imaging,exoplanet,adaptive optics,atmospheric turbulence,high-resolution imaging
更新于2025-09-10 09:29:36
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Fast Restoration of Aberration-Degraded Extended Object Based on Local Region Abstraction
摘要： The compensating capability of wavefront sensorless adaptive optics (WFSless AO) system for extended object images degraded by aberration is severely limited to correction speed due to largely sized images and low frame rate of camera. To improve the correction capability of WFSless AO system, a method based on local region abstraction (LRA) is presented according to the sparse characteristics of extended object imaging. The experiment results of image restoration with WFSless AO system based on LRA show that the correction speed of this method is 8–20 times faster than that of the previous method for the static aberration, the image restoration speed is improved by about 3.5 times under the dynamic aberration.
关键词： image restoration,correction speed,Adaptive optics system,LRA,aberration
更新于2025-09-10 09:29:36
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Daytime optical turbulence and wind speed distributions at the Baikal Astrophysical Observatory
摘要： Atmospheric turbulence limits the angular resolution of ground-based optical telescopes. The daytime turbulence conditions for solar observations are stronger and more complicated than the turbulence observed at night. The Baikal Astrophysical Observatory is the site of the 1-m Large Solar Vacuum Telescope (LSVT) located near Lake Baikal (East Siberia, Russia), which is the largest freshwater lake in the world. The region hosts unique weather regimes and natural phenomena, including local winds and giant ice rings. Because the LSVT has ongoing and planned programmes in adaptive optics (AO), statistical knowledge of atmospheric turbulence and wind speed distributions is essential for designing and optimizing AO systems. We present the first seasonal study of the vertical distribution of wind speed and daytime optical turbulence conditions at the Baikal Astrophysical Observatory. Site measurements of the daytime Fried parameter were collected using the Shack–Hartmann wavefront sensor in the LSVT AO system. Reanalysis data from the National Centers for Environmental Prediction (NCEP) and the National Centers for Atmospheric Research (NCAR) were used to characterize the wind speed distribution. The results demonstrate seasonal variation in both solar seeing and wind speed profile. The strongest wind speed was detected in winter and in November, while the weakest wind speed occurred during summer. The strongest daytime turbulence conditions were observed in the winter. The best solar seeing β0 ≈ 1 arcsec was detected in the summer.
关键词： site testing,atmospheric effects,instrumentation: adaptive optics
更新于2025-09-10 09:29:36
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Pulsation Characteristics of Jovian Infrared Northern Aurora Observed by the Subaru IRCS with Adaptive Optics
摘要： We report narrow band-?ltered imaging observations of the Jovian H3+ 3.4-μm emission using the IRCS (infrared camera and spectrograph) on the Subaru telescope taken on 25 May 2016. Approximately 1 hr of data was taken at intervals of 45–110 s, with high spatial resolution (~0.2 arcsec) using adaptive optics. In the northern polar region, we found bright patch-like emissions on the poleward side of the main oval. One of them had a pulsation period of ~10 min. We utilized an H3+ emission model to investigate the response time of the H3+ emission to abrupt and periodic variations of the precipitating electron ?ux. The model showed that the H3+ emission could pulsate with this timescale due to a modulated ?ux of the precipitating electrons in the kilo-electron-volt to tens of kilo-electron-volt energy range.
关键词： adaptive optics,H3+,Subaru telescope,infrared emission,Jovian aurora
更新于2025-09-10 09:29:36
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Vortex instability in turbulent free-space propagation
摘要： The spatial structuring of optical fields is integral within many next generation optical metrology and communication techniques. A verifiable physical model of the propagation of these optical fields in a turbulent environment is important for developing effective mitigation techniques for the modal degradation that occurs in a free-space link. We present a method to simulate this modal degradation that agrees with recently reported experimental findings. A 1.5 km free-space link is emulated by decomposing the optical turbulence that accumulates over a long distance link, into many, weakly perturbing steps of 10 m. This simulation shows that the high-order vortex at the centre of the helical phase profiles in modes that carry orbital angular momentum of ? are unstable and fracture into many vortices when they propagate over the link. This splitting presents issues for the application of turbulence mitigation techniques. The usefulness of pre-correction, post-correction, and complex field conjugation techniques are discussed.
关键词： optical propagation,orbital angular momentum,adaptive optics,optical vortices,atmospheric turbulence
更新于2025-09-09 09:28:46
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A new calibration strategy for adaptive telescopes with pyramid WFS
摘要： Several telescopes include large deformable mirrors (DM) located directly inside the telescope. These adaptive telescopes trigger new constraints for the calibration of the adaptive optics (AO) systems as they usually offer no access to an artificial calibration source for the interaction matrix measurement. Moreover, the optical propagation between the DM and the wavefront sensor (WFS) may evolve during the operation, resulting in misregistrations that highly affect the AO performance and thus the scientific observation. They have to be measured and compensated, for instance by updating the calibration. A new strategy consists of estimating the misregistrations and injecting them into synthetic models to generate noise-free interaction matrices. This pseudo-synthetic approach is the baseline for the adaptive optics facility working with a Shack–Hartmann WFS and seems particularly suited for the future Extremely Large Telescope as the calibration will have to be regularly updated, for a large numbers of actuators. In this paper, the feasibility of a pseudo-synthetic calibration with pyramid WFS at the Large Binocular Telescope (LBT) is investigated. A synthetic model of the LBT AO systems is developed, and the procedure to adjust the misregistrations parameters is introduced, extracting them from an experimental interaction matrix. We successfully tested an interaction matrix generated from the model on the real system in high-order AO mode. We recorded a slightly better performance with respect to the experimental one. This work demonstrates that a high-accuracy calibration can be obtained using the pseudo-synthetic approach with pyramid WFS.
关键词： telescopes,instrumentation: adaptive optics
更新于2025-09-09 09:28:46
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The Negative Cone Mosaic: A New Manifestation of the Optical Stiles-Crawford Effect in Normal Eyes
摘要： The purpose of this study was to describe a previously unreported manifestation of the optical Stiles-Crawford effect (oSCE) in normal eyes. In a cohort of 50 normal subjects, the directional reflectance of cones in the retinal periphery was explored by flood-illuminated adaptive optics (FIAO) and optical coherence tomography (OCT). In 32 eyes (64%), off-axis FIAO images of the retinal periphery (~15–208 from the fovea) showed variably sized patches of hyporeflective dots (called here negative mosaic) coexisting with hyperreflective (positive) cones. In nine cases, shifting the entry pupil toward the optical axis restored the positive cone mosaic, with a point-by-point correspondence between positive and negative mosaics. Rods remained hyperreflective around negative and positive cones. These changes were paralleled by changes of the OCT reflectance of the cone outer segment tips and, to a lesser extent, of the inner/outer segment limit. By en face FIAO imaging of the retina, the contrast of cones over rods may be strongly dependent on the entry pupil to such an extent that their reflectance is lower than that of rods. We hypothesized that the negative cone mosaic aspect results from the differential Stiles-Crawford effect of cones and rods. Cone reflectance by en face FIAO parallels the reflectance from the cone outer segment tip line and to a lesser extent of the inner/outer segment limit by OCT. Taking this into account, the oSCE is of importance for the interpretation of high-resolution images of photoreceptors.
关键词： photoreceptors,adaptive optics,optical coherence tomography,optical Stiles-Crawford effect
更新于2025-09-09 09:28:46
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Human Retinal Pigment Epithelium: In Vivo Cell Morphometry, Multispectral Autofluorescence, and Relationship to Cone Mosaic
摘要： PURPOSE. To characterize in vivo morphometry and multispectral autofluorescence of the retinal pigment epithelial (RPE) cell mosaic and its relationship to cone cell topography across the macula. METHODS. RPE cell morphometrics were computed in regularly spaced regions of interest (ROIs) from contiguous short-wavelength autofluorescence (SWAF) and photoreceptor reflectance images collected across the macula in one eye of 10 normal participants (23–65 years) by using adaptive optics scanning light ophthalmoscopy (AOSLO). Infrared autofluorescence (IRAF) images of the RPE were collected with AOSLO in seven normal participants (22–65 years), with participant overlap, and compared to SWAF quantitatively and qualitatively. RESULTS. RPE cell statistics could be analyzed in 84% of SWAF ROIs. RPE cell density consistently decreased with eccentricity from the fovea (participant mean 6 SD: 6026 6 1590 cells/mm2 at fovea; 4552 6 1370 cells/mm2 and 3757 6 1290 cells/mm2 at 3.5 mm temporally and nasally, respectively). Mean cone-to-RPE cell ratio decreased rapidly from 16.6 at the foveal center to <5 by 1 mm. IRAF revealed cells in six of seven participants, in agreement with SWAF RPE cell size and location. Differences in cell fluorescent structure, contrast, and visibility beneath vasculature were observed between modalities. CONCLUSIONS. Improvements in AOSLO autofluorescence imaging permit efficient visualization of RPE cells with safe light exposures, allowing individual characterization of RPE cell morphometry that is variable between participants. The normative dataset and analysis of RPE cell IRAF and SWAF herein are essential for understanding microscopic characteristics of cell fluorescence and may assist in interpreting disease progression in RPE cells.
关键词： autofluorescence,retinal imaging,photoreceptors,retinal pigment epithelium,adaptive optics
更新于2025-09-09 09:28:46
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High-contrast imaging in polychromatic light with the self-coherent camera
摘要： Context. In the context of direct imaging of exoplanets, coronagraphs are commonly proposed to reach the required very high contrast levels. However, wavefront aberrations induce speckles in their focal plane and limit their performance. Aims.An active correction of these wavefront aberrations using a deformable mirror upstream of the coronagraph is mandatory. These aberrations need to be calibrated and focal-plane wavefront-sensing techniques in the science channel are being developed. One of these is the self-coherent camera, of which we present the latest laboratory results. Methods. We present here an enhancement of the method: we directly minimized the complex amplitude of the speckle ?eld in the focal plane. Laboratory tests using a four-quadrant phase-mask coronagraph and a 32 × 32 actuator deformable mirror were conducted in monochromatic light and in polychromatic light for di?erent bandwidths. Results. We obtain contrast levels in the focal plane in monochromatic light better than 3 × 10?8 (RMS) in the 5–12 λ/D region for a correction of both phase and amplitude aberrations. In narrow bands (10 nm) the contrast level is 4 × 10?8 (RMS) in the same region. Conclusions. The contrast level is currently limited by the amplitude aberrations on the bench. We identi?ed several improvements that can be implemented to enhance the performance of our optical bench in monochromatic as well as in polychromatic light.
关键词： instrumentation: adaptive optics,instrumentation: high angular resolution
更新于2025-09-04 15:30:14
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Confocal Adaptive Optics Imaging of Peripapillary Nerve Fiber Bundles: Implications for Glaucomatous Damage Seen on Circumpapillary OCT Scans
摘要： To improve our understanding of glaucomatous damage as seen on circumpapillary disc scans obtained with frequency-domain optical coherence tomography (fdOCT), fdOCT scans were compared to images of the peripapillary retinal nerve fiber (RNF) bundles obtained with an adaptive optics-scanning light ophthalmoscope (AO-SLO). The AO-SLO images and fdOCT scans were obtained on 6 eyes of 6 patients with deep arcuate defects (5 points (cid:2)(cid:3)15 db) on 10-2 visual fields. The AO-SLO images were montaged and aligned with the fdOCT images to compare the RNF bundles seen with AO-SLO to the RNF layer thickness measured with fdOCT. All 6 eyes had an abnormally thin (1% confidence limit) RNF layer (RNFL) on regions of RNF bundles on AO-SLO in fdOCT and abnormal corresponding regions. However, regions of abnormal, but equal, RNFL thickness on fdOCT scans varied in appearance on AO-SLO images. These regions could be largely devoid of RNF bundles (5 eyes), have abnormal-appearing bundles of lower contrast (6 eyes), or have isolated areas with a few relatively normal-appearing bundles (2 eyes). There also were local variations in reflectivity of the fdOCT RNFL that corresponded to the variations in AO-SLO RNF bundle appearance. Relatively similar 10-2 defects with similar fdOCT RNFL thickness profiles can have very different degrees of RNF bundle damage as seen on fdOCT and AO-SLO. While the results point to limitations of fdOCT RNFL thickness as typically analyzed, they also illustrate the potential for improving fdOCT by attending to variations in local intensity.
关键词： optical coherence tomography,retinal nerve fiber layer,glaucoma,adaptive optics,optic disc
更新于2025-09-04 15:30:14