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A High-precision Technique to Correct for Residual Atmospheric Dispersion in High-contrast Imaging Systems
摘要： Direct detection and spectroscopy of exoplanets requires high-contrast imaging. For habitable exoplanets in particular, located at a small angular separation from the host star, it is crucial to employ small inner working angle (IWA) coronagraphs that ef?ciently suppress starlight. These coronagraphs, in turn, require careful control of the wavefront that directly impacts their performance. For ground-based telescopes, atmospheric refraction is also an important factor, since it results in a smearing of the point-spread function (PSF), that can no longer be ef?ciently suppressed by the coronagraph. Traditionally, atmospheric refraction is compensated for by an atmospheric dispersion compensator (ADC). ADC control relies on an a priori model of the atmosphere whose parameters are solely based on the pointing of the telescope, which can result in imperfect compensation. For a high-contrast instrument like the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, which employs very small IWA coronagraphs, refraction-induced smearing of the PSF has to be less than 1 mas in the science band for the ?rst on-sky measurement and correction of residual optimum performance. In this paper, we present atmospheric dispersion. Atmospheric dispersion is measured from the science image directly, using an adaptive grid of arti?cially introduced speckles as a diagnostic to feedback to the telescope’s ADC. With our current setup, we were able to reduce the initial residual atmospheric dispersion from 18.8 mas to 4.2 in broadband light (y- to H-band) and to 1.4 mas in the H-band only. This work is particularly relevant to the upcoming extremely large telescopes (ELTs) that will require ?ne control of their ADC to reach their full high-contrast imaging potential.
关键词： atmospheric effects,planets and satellites: detection,instrumentation: adaptive optics
更新于2025-09-04 15:30:14
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Imaging Glaucomatous Damage Across the Temporal Raphe
摘要： PURPOSE. To image and analyze anatomical differences at the temporal raphe between normal and glaucomatous eyes using adaptive optics scanning laser ophthalmoscopy (AOSLO) and optical coherence tomography (OCT), and to relate these differences to visual ?eld measurements. METHODS. Nine glaucomatous eyes of 9 patients (age 54–78 years, mean deviation of visual ?eld [MD] (cid:2)5.03 to (cid:2)0.20 dB) and 10 normal eyes of 10 controls (age 54–81, MD (cid:2)1.13 to t1.39 dB) were enrolled. All the participants were imaged in a region that was centered approximately 98 temporal to the fovea. The size of imaging region was at least 108 vertically by 48 horizontally. The raphe gap, de?ned as the distance between the superior and inferior retinal nerve ?ber layer (RNFL) bundles, was measured. A bundle index was computed to quantify the relative re?ectivity and density of the nerve ?ber bundles. We also measured thickness of the ganglion cell complex (GCC) and RNFL. RESULTS. The raphe gap was larger in glaucomatous eyes than control eyes. Speci?cally, eight glaucomatous eyes with local averaged ?eld loss no worse than (cid:2)3.5 dB had larger raphe gaps than all control eyes. The bundle index, GCC thickness, and RNFL thickness were on average reduced in glaucomatous eyes, with the ?rst two showing statistically signi?cant differences between the two groups. CONCLUSIONS. Structural changes in the temporal raphe were observed and quanti?ed even when local functional loss was mild. These techniques open the possibility of using the raphe as a site for glaucoma research and clinical assessment.
关键词： visual ?eld,OCT,raphe,glaucoma,adaptive optics
更新于2025-09-04 15:30:14
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Accommodation Responds to Optical Vergence and Not Defocus Blur Alone
摘要： To determine whether changes in wavefront spherical curvature (optical vergence) are a directional cue for accommodation. Nine subjects participated in this experiment. The accommodation response to a monochromatic target was measured continuously with a custom-made adaptive optics system while astigmatism and higher-order aberrations were corrected in real time. There were two experimental open-loop conditions: vergence-driven condition, where the deformable mirror provided sinusoidal changes in defocus at the retina between (cid:2)1 and t1 diopters (D) at 0.2 Hz; and blur-driven condition, in which the level of defocus at the retina was always 0 D, but a sinusoidal defocus blur between (cid:2)1 and t1 D at 0.2 Hz was simulated in the target. Right before the beginning of each trial, the target was moved to an accommodative demand of 2 D. Eight out of nine subjects showed sinusoidal responses for the vergence-driven condition but not for the blur-driven condition. Their average (6SD) gain for the vergence-driven condition was 0.50 (60.28). For the blur-driven condition, average gain was much smaller at 0.07 (60.03). The ninth subject showed little to no response for both conditions, with average gain <0.08. Vergence-driven condition gain was significantly different from blur-driven condition gain (P ? 0.004). Accommodation responds to optical vergence, even without feedback, and not to changes in defocus blur alone. These results suggest the presence of a retinal mechanism that provides a directional cue for accommodation from optical vergence.
关键词： accommodation,vergence,defocus blur,adaptive optics,dynamic accommodation
更新于2025-09-04 15:30:14