- 标题
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Assessment of Different Sampling Methods for Measuring and Representing Macular Cone Density Using Flood-Illuminated Adaptive Optics
摘要： PURPOSE. To describe a standardized flood-illuminated adaptive optics (AO) imaging protocol suitable for the clinical setting and to assess sampling methods for measuring cone density. METHODS. Cone density was calculated following three measurement protocols: 50 × 50-μm sampling window values every 0.5° along the horizontal and vertical meridians (fixed-interval method), the mean density of expanding 0.5°-wide arcuate areas in the nasal, temporal, superior, and inferior quadrants (arcuate mean method), and the peak cone density of a 50 × 50-μm sampling window within expanding arcuate areas near the meridian (peak density method). Repeated imaging was performed in nine subjects to determine intersession repeatability of cone density. RESULTS. Cone density montages could be created for 67 of the 74 subjects. Image quality was determined to be adequate for automated cone counting for 35 (52%) of the 67 subjects. We found that cone density varied with different sampling methods and regions tested. In the nasal and temporal quadrants, peak density most closely resembled histological data, whereas the arcuate mean and fixed-interval methods tended to underestimate the density compared with histological data. However, in the inferior and superior quadrants, arcuate mean and fixed-interval methods most closely matched histological data, whereas the peak density method overestimated cone density compared with histological data. Intersession repeatability testing showed that repeatability was greatest when sampling by arcuate mean and lowest when sampling by fixed interval. CONCLUSIONS. We show that different methods of sampling can significantly affect cone density measurements. Therefore, care must be taken when interpreting cone density results, even in a normal population.
关键词： cone photoreceptor density,retina,adaptive optics
更新于2025-09-23 15:23:52
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Using the multi-object adaptive optics demonstrator RAVEN to observe metal-poor stars in and towards the Galactic Centre
摘要： The chemical abundances for five metal-poor stars in and towards the Galactic bulge have been determined from the H-band infrared spectroscopy taken with the RAVEN multi-object adaptive optics science demonstrator and the Infrared Camera and Spectrograph at the Subaru 8.2-m telescope. Three of these stars are in the Galactic bulge and have metallicities between ?2.1 < [Fe/H] < ?1.5, and high [α/Fe] ～ +0.3, typical of Galactic disc and bulge stars in this metallicity range; [Al/Fe] and [N/Fe] are also high, whereas [C/Fe] < +0.3. An examination of their orbits suggests that two of these stars may be confined to the Galactic bulge and one is a halo trespasser, though proper motion values used to calculate orbits are quite uncertain. An additional two stars in the globular cluster M22 show [Fe/H] values consistent to within 1σ, although one of these two stars has [Fe/H] = ?2.01 ± 0.09, which is on the low end for this cluster. The [α/Fe] and [Ni/Fe] values differ by 2σ, with the most metal-poor star showing significantly higher values for these elements. M22 is known to show element abundance variations, consistent with a multipopulation scenario though our results cannot discriminate this clearly given our abundance uncertainties. This is the first science demonstration of multi-object adaptive optics with high-resolution infrared spectroscopy, and we also discuss the feasibility of this technique for use in the upcoming era of 30-m class telescope facilities.
关键词： stars: abundances,Galaxy: centre,instrumentation: adaptive optics,globular clusters: individual: M22,techniques: spectroscopic
更新于2025-09-23 15:23:52
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Cone–Photoreceptor Density in Adolescents With Type 1 Diabetes
摘要： Changes to retinal structure and function occur in individuals with diabetes before the onset of diabetic retinopathy. It is still unclear if these changes initially affect vascular or neural retina, or if particular retinal areas are more susceptible than others. This paper examines the distribution of cone photoreceptor density in the retina of adolescents with type 1 diabetes. This cross-sectional prospective study includes 29 adolescents and young adults with type 1 diabetes and no diabetic retinopathy and 44 control participants recruited at the Hospital for Sick Children. Adaptive-optics enhanced retinal imaging of the cone photoreceptor mosaic was performed in four quadrants at an eccentricity of ~78 from the fovea. After image registration and averaging, cone photoreceptors were counted and photoreceptor density was calculated. Analysis of variance with repeated measures was used to assess the differences in photoreceptor density between groups. Cone density was similar in both control participants and participants with diabetes. There was a small effect of retinal hemisphere; participants with diabetes did not show the expected radial asymmetry observed in control participants. Cone density in the parafoveal retina is not reduced in adolescents with type 1 diabetes.
关键词： adolescent,retina,type 1 diabetes,adaptive optics
更新于2025-09-23 15:23:52
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High resolution mesospheric sodium properties for adaptive optics applications
摘要： Context. The performance of laser guide star adaptive optics (AO) systems for large optical and infrared telescopes is affected by variability of the sodium layer, located at altitudes between 80 and 120 km in the upper mesosphere and lower thermosphere. The abundance and density structure of the atomic sodium found in this region is subject to local and global weather effects, planetary and gravity waves and magnetic storms, and is variable on time scales down to tens of milliseconds, a range relevant to AO. Aims. It is therefore important to characterize the structure and dynamical evolution of the sodium region on small, as well as large spatial and temporal scales. Parameters of particular importance for AO are the mean sodium altitude, sodium layer width and the temporal power spectrum of the centroid altitude. Methods. We have conducted a three-year campaign employing a high-resolution lidar system installed on the 6-m Large Zenith Telescope (LZT) located near Vancouver, Canada. During this period, 112 nights of useful data were obtained. Results. The vertical density profile of atomic sodium shows remarkable structure and variability. Smooth Gaussian-shaped profiles rarely occur. Multiple internal layers are frequently found. These layers often have sharp lower edges, with scale heights of just a few hundred meters, and tend to drift downwards at a typical rate of one kilometer every two to three hours. Individual layers can persist for many hours, but their density and internal structure can be highly variable. Sporadic layers are seen reaching peak densities several times the average, often in just a few minutes. Coherent vertical oscillations are often found, typically extending over tens of kilometers in altitude. Regions of turbulence are evident and Kelvin-Helmholtz instability are sometimes seen. The mean value of the centroid altitude is found to be 90.8 ± 0.1 km. The sodium layer width was determined by computing the altitude range that contains a specified fraction of the returned sodium light. We find a mean value of 13.1 ± 0.3 km for the range containing 95% of the photons, with a maximum width of 21 km. The temporal power spectral density of fluctuations of the centroid altitude is well described by a power law having an index that ranges from ?1.6 to ?2.3 with a mean value of ?1.87 ± 0.02. This is significantly steeper than the value of ?5/3 that would be expected if the dynamics were dominated by Kolmogorov turbulence, indicating that other factors such as gravity waves play an important role. The amplitude of the power spectrum has a mean value of 34+6?5 m2 Hz?1 at a frequency of 1 Hz, but ranges over two orders of magnitude. The annual means of the index and amplitude show a variation that is well beyond the calculated error range. Long-term global weather patterns may be responsible for this effect.
关键词： site testing,atmospheric effects,methods: observational,instrumentation: adaptive optics
更新于2025-09-23 15:23:52
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SPHERE/ZIMPOL high resolution polarimetric imager
摘要： Context. The SPHERE “planet finder” is an extreme adaptive optics (AO) instrument for high resolution and high contrast observations at the Very Large Telescope (VLT). We describe the Zurich Imaging Polarimeter (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance. Aims. We present a detailed characterization of SPHERE/ZIMPOL which should be useful for an optimal planning of observations and for improving the data reduction and calibration. We aim to provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging. Methods. We have analyzed SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and the peak flux attenuation and the off-axis flux transmission are determined. Simultaneous images of the coronagraphic focal plane and the pupil plane are analyzed and the suppression of the diffraction rings by the pupil stop is investigated. We compared the performance at small separation for different coronagraphs with tests for the binary α Hyi with a separation of 92 mas and a contrast of Δm ≈ 6m. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show small (<1 mas) but disturbing differential polarimetric beam shifts, which can be explained as Goos-H?nchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr. Results. SPHERE/ZIMPOL reaches routinely an angular resolution (FWHM) of 22?28 mas, and a normalized peak surface brightness of SB0 ? mstar ≈ ?6.5m arcsec?2 for the V-, R- and I-band. The AO performance is worse for mediocre (?1.0″) seeing conditions, faint stars mR ? 9m, or in the presence of the “low wind” effect (telescope seeing). The coronagraphs are effective in attenuating the PSF peak by factors of >100, and the suppression of the diffracted light improves the contrast performance by a factor of approximately two in the separation range 0.06″?0.20″. The polarimetric sensitivity is Δp < 0.01% and the polarization zero point can be calibrated to better than Δp ≈ 0.1%. The contrast limits for differential polarimetric imaging for the 400 s I-band data of R Aqr at a separation of ρ = 0.86″ are for the surface brightness contrast SBpol(ρ)?mstar ≈ 8m arcsec?2 and for the point source contrast mpol(ρ)?mstar ≈ 15m and much lower limits are achievable with deeper observations. Conclusions. SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar Hα emission.
关键词： circumstellar matter,instrumentation: adaptive optics,planetary systems,instrumentation: polarimeters,instrumentation: high angular resolution,instrumentation: detectors
更新于2025-09-23 15:23:52
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Rapid tomographic reconstruction through GPU-based adaptive optics
摘要： Large telescopes have important challenges in the near future. Increasing the size of mirrors and sensors suppose not only a design issue, but also new computational techniques are needed to deal with the large amount of data. Adaptive Optics is an essential part of extremely large telescopes, and it uses reference stars and a tomographic reconstructor to compensate the aberrations introduced by the atmosphere during observation. The Complex Atmospheric Reconstructor based on Machine lEarNing (CARMEN) is a tomographic reconstructor based on neural networks which has been used during on-sky observations. In this paper CARMEN will be implemented in two different neural network frameworks, which use a Graphics Processing Unit to improve their performance. To time the training and execution will provide results of which framework is faster for its implementation in a real telescope and will supply new tools to keep improving the reconstruction ability of CARMEN.
关键词： Adaptive Optics,Torch,Neural Networks,TensorFlow
更新于2025-09-23 15:23:52
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Characterizing daytime wind profiles with the wide-field Shack–Hartmann wavefront sensor
摘要： Knowledge of the vertical spatio-temporal distribution of the wind speed and direction is essential for optimizing the performance of adaptive optics systems. An extension of SLODAR (slope detection and ranging) can be used for wind profiling by tracking the time-delayed cross-correlation peaks obtained from the slope of the Shack–Hartmann wavefront sensor. This wind-profiling method works well in situations where the cross-correlation peaks can be individualized, but in many cases the isolated cross-correlation peaks for each turbulent layer are difficult to find in the 2D cross-correlation maps, which can result in difficulties when estimating the wind profiles. To address this problem, we propose a method to measure the wind speed and direction of each layer. The method distinguishes isolated peaks more easily and is valid for multiple peaks, even for a weak response. Instead of tracking peaks in 2D cross-correlation maps, the proposed method traces a series of cross-correlation peaks in the curves of 1D slices through the maps from different directions, and finally determines the wind speed and direction according to the frozen-flow hypothesis. This method is verified with simulations, in which the input wind profiles are recovered accurately. Furthermore, this method is applied to 47 data sequences from the 1-m New Vacuum Solar Telescope at Fuxian Solar Observatory. The wind profiles are estimated from the ground up to 12 km, and the experimental results show that all layers move with a relatively low speed.
关键词： Sun: granulation,atmospheric effects,instrumentation: adaptive optics
更新于2025-09-23 15:23:52
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[IEEE 2017 IEEE International Conference on Space Optical Systems and Applications (ICSOS) - Naha (2017.11.14-2017.11.16)] 2017 IEEE International Conference on Space Optical Systems and Applications (ICSOS) - Adaptive optics pre-compensation for GEO feeder links: Towards an experimental demonstration
摘要： High throughput ground to satellite telecommunication systems will require very capacitive links for the uplink. When diffraction limited, a few optical Watts per channel are sufficient to close the link budget. In the presence of atmospheric turbulence, higher emission powers are necessary to cope with the subsequent disruptions of the beam. Pre-compensation by adaptive optics has been identified as a key strategy to keep the requested power at reasonable levels. However limited by point-ahead anisoplanatism. Fine trade-offs shall be carried out to overcome this limitation while considering the specificities of optical telecommunication requirements (low fading probably, short fading duration, manageable cost and complexity). The expected performance of the pre-compensation by adaptive optics for optical feeder links is investigated through numerical simulations. A ground-to-ground experimental demonstration is proposed. The selected slant line of sight and the beam geometry is shown to induce turbulence effects, including angular decorrelation, that are representative of the GEO feeder link scenario when considering an appropriate setup.
关键词： anisoplanatism,adaptive optics,ground to satellite laser links
更新于2025-09-23 15:22:29
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Characterizing the Performance of the NIRC2 Vortex Coronagraph at W. M. Keck Observatory
摘要： The NIRC2 vortex coronagraph is an instrument on Keck II designed to directly image exoplanets and circumstellar disks at mid-infrared bands L′ (3.4–4.1 μm) and Ms (4.55–4.8 μm). We analyze imaging data and corresponding adaptive optics telemetry, observing conditions, and other metadata over a three-year time period to characterize the performance of the instrument and predict the detection limits of future observations. We systematically process images from 359 observations of 304 unique stars to subtract residual starlight (i.e., the coronagraphic point-spread function) of the target star using two methods: angular differential imaging (ADI) and reference star differential imaging (RDI). We ?nd that for the typical parallactic angle (PA) rotation of our data set (～10°), RDI provides gains over ADI for angular separations smaller than 0 25. Furthermore, we ?nd a power-law relation between the angular separation from the host star and the minimum PA rotation required for ADI to outperform RDI, with a power-law index of ?1.18 ± 0.08. Finally, we use random forest models to estimate ADI and RDI post-processed detection limits a priori. These models, which we provide publicly on a website, explain 70%–80% of the variance in ADI detection limits and 30%–50% of the variance in RDI detection limits. Averaged over a range of angular separations, our models predict both ADI and RDI contrast to within a factor of 2. These results illuminate important factors in high-contrast imaging observations with the NIRC2 vortex coronagraph, help improve observing strategies, and inform future upgrades to the hardware.
关键词： planets and satellites: detection,instrumentation: adaptive optics
更新于2025-09-23 15:22:29
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Dynamic response of ferrofluidic deformable mirrors using elastomer membrane and overdrive techniques
摘要： The experimental results obtained with a ferrofluidic deformable mirror controlled by electro-magnet actuators are presented here. Using a step input through a single actuator, we obtained a steady-state settling time of 100 ms; however, different combinations of overdrive inputs can be used to decrease it to 25 ms. A new technique which consists of laying down an elastomer membrane, coated with an aluminum film, on the ferrofluid is also discussed. By adding the membrane on the ferrofluid, it further decreases the time response by a factor of 2. Furthermore, the thin aluminum layer improves the reflectivity of the mirror. Finally, using the membrane and the overdrive techniques combined, the time response is improved by a factor of 20. Numerical simulations show that ferrofluidic mirrors using membranes and improved electronics should reach settling times of the order of a millisecond. Presumably, even lower settling times could be possible.
关键词： physical optics,optical components,Adaptive optics
更新于2025-09-23 15:21:01