Adaptive optics: a progress review
TL;DR: Active and adaptive optics technology has emerged from the laboratory and is being applied to improve the performance of optical imaging and laser systems as mentioned in this paper, among which are high-performance deformable mirrors, new types of wavefront sensors, and more sophisticated wavefront processing algorithms.
Abstract: Active and adaptive optics technology has emerged from the laboratory and is being applied to improve the performance of optical imaging and laser systems. In the last few years, development of both systems and components has accelerated. Many new concepts and devices have appeared, among which are high-performance deformable mirrors, new types of wavefront sensors, and more sophisticated wavefront processing algorithms. Equally important, a better understanding of the system design aspects of adaptive optics has been reached, particularly of the need for optimizing each system according to its application. For example, the dominant requirement in laser systems is to achieve a high Strehl ratio, whereas for ground-based astronomy the availability of guide stars is a major concern. Current developments in adaptive optics for ground-based astronomy include the use of IR wavelengths, partial wavefront compensation using natural guide stars, and the use of laser guide stars to allow all-sky coverage with full compensation at visible wavelengths. While progress to date has been impressive, much work remains to bring this technology into general use.
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TL;DR: An experiment over a 5.5-km horizontal propagation path to explore the efficacy of conventional adaptive optics in strong-scintillation conditions showed a significant degradation in correction as the scintillation increased.
Abstract: Most atmospheric-turbulence-compensation experiments have been performed under weak-scintillation conditions; conventional phase-conjugate adaptive-optics systems usually provide good correction for these conditions. We have performed an experiment over a 5.5-km horizontal propagation path to explore the efficacy of conventional adaptive optics in strong-scintillation conditions. The experimental results showed a significant degradation in correction as the scintillation increased. The presence of branch points in the phase appears to be the primary reason for the degradation in correction as the scintillation increases.
103 citations
TL;DR: A review of the early and present periods of research in aero-optics can be found in this article, which traces the activities and developments associated with both periods but particularly focuses on the development of modern high-bandwidth wavefront sensors used in the present research period.
Abstract: The field of aero-optics is devoted to the study of the effects of turbulent flow fields on laser beams projected from airborne laser systems. This article reviews the early and present periods of research in aero-optics. Both periods generated impressive amounts of research activity; however, the types and amount of data differ greatly in accuracy, quality, and type owing to the development of new types of instrumentation available to collect and analyze the aberrated wave fronts of otherwise collimated laser beams projected through turbulent compressible flow fields of the type that form over beam directors. This review traces the activities and developments associated with both periods but particularly focuses on the development of modern high-bandwidth wave-front sensors used in the present research period. We describe how these modern wave-front data are collected and analyzed and the fluid mechanic information that can be gleaned from them; the use of these data in the fundamental study of turbulenc...
99 citations
TL;DR: In this paper, the spatial and temporal characterizations of phase fluctuations in non-Kolmogorov turbulence were analyzed and the generalized coherence length rho(0), the characteristic frequency f(R), and the characteristic time tau(R) were derived.
Abstract: Atmospheric turbulence severely limits the performance of ground-based imaging and laser propagation systems. Some observational results, showing atmospheric turbulence which does not obey Kolmogorov's theory, have prompted the study of optical propagation through non-Kolmogorov turbulence. This paper presents a theoretical approach to analyse the spatial and temporal characterizations of phase fluctuations in non-Kolmogorov turbulence. The spatial structure function, the temporal structure function and the temporal power spectrum of phase fluctuations are derived. The generalized coherence length rho(0), the characteristic frequency f(R) and the characteristic time tau(R) are expressed as functions of the index structure constant along the propagation path and the wind velocity. The long exposure MTF, the short exposure MTF and the imaging Strehl ratio are computed.
94 citations
TL;DR: The measurement accuracy and reproducibility of the Shack Hartmann wave-front sensor are better than λ/20 andλ/50 (λ = 632.8 nm),respectively, in rms.
Abstract: A new plastic microlens array, consisting of 900 lenslets, has been developed for the Shack Hartmann wave-front sensor. The individual lens is 300 μm × 300 μm and has a focal length of 10 mm, which provides the same focal size, 60 μm in diameter, with a constant peak intensity. One can improve the wave-front measurement accuracy by reducing the spot centroiding error by averaging a few frame memories of an image processor. A deformable mirror for testing the wave-front sensor gives an appropriate defocus and astigmatism, and the laser wave front is measured with a Shack Hartmann wave-front sensor. The measurement accuracy and reproducibility of our wave-front sensor are better than λ./20 and λ/50 (λ = 632.8 nm), respectively, in rms.
83 citations
TL;DR: In this paper, a lateral shear interferometer is used for obtaining shearograms of optical fields with vortices and a diffractive phase element is used to generate vortice.
20 citations