Topic
Spatial filter
About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.
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Papers
More filters
TL;DR: Hemmer et al. as discussed by the authors proposed a nonspatial filter based on the Bragg selectivity of thick holograms, which eliminates the need for laser beam focusing, which is the source of material and alignment instabilities and laser power limitations of spatial filters.
Abstract: Philip Hemmer, MEMBER SPIE Rome Laboratory RL/EROP, 63 Scott Road Hanscom Air Force Base, Massachusetts 01731 Abstract. A novel device, the nonspatial filter, is described for laser beam cleanup. It is based on the Bragg selectivity of thick holograms. Unlike pinhole and fiber spatial filters, which employ lenses and apertures in the transform plane, nonspatial filters operate directly on the laser beam. This eliminates the need for laser beam focusing, which is the source of many of the material and alignment instabilities and laser power limitations of spatial filters. Standard holographic materials are not suitable for this application because differential shrinkage during processing limits the maximum Bragg angle selectivity attainable, and because they are generally too thin. New technologies that eliminate the problem of differential shrinkage are described. These technologies are based either on the use of a rigid porous substrate material, such as porous glass, filled with a light-sensitive material, such as holographic photopolymers or dichromated gelatin, or on the use of a thick photopolymer with diffusion amplification (PDA). We report results of holographic nonspatial filtering of a laser beam in one dimension, with an angular selectivity of better than 1 mrad. © 1997 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(97)01606-1]
68 citations
TL;DR: This paper explains, demonstrates, and explores a new approach to optical processing, in which the essentially coherent operations lacked by incoherent optics are performed electronically.
Abstract: Once it is appreciated that a lens imaging with spatially incoherent light may be interpreted as a spatial filter, it is natural to ask what freedom exists in lens design to implement an arbitrary filter function (or OTF, as it is known). Specifically, is it possible to implement OTFs for specialized data processing operations, such as radar pulse compression or deblurring radiographic images? The conventional answer to such questions is negative; the answer becomes affirmative if a hybrid approach is followed. This approach departs significantly from conventional optical processing, since it exploits the diffraction of light emanating from a spatially incoherent source. Two advantages follow: (1) resistance to noise and (2) relaxed requirements on input and output devices. It is the purpose of this paper to explain, demonstrate, and explore this new approach to optical processing, in which the essentially coherent operations lacked by incoherent optics are performed electronically.
67 citations
TL;DR: A filter combination consisting of a lens and two pure phase filters, situated in the two focal planes, that apparently does not absorb any light and is capable of shaping wave fronts with 100% efficiency independent of the object function is discussed.
Abstract: A filter combination consisting of a lens and two pure phase filters, situated in the two focal planes, is discussed. This element, which we call a tandem component, apparently does not absorb any light; in other words, the tandem component is capable of shaping wave fronts with 100% efficiency independent of the object function. We describe a basic configuration and outline its space-variant system properties. The tandem component can be used for many of the standard applications of computer-generated holograms and possibly for some new types as well in view of its space variance.
67 citations
TL;DR: In this article, a control technique for spatially extended systems combining spatial filtering with a previously studied form of time-delay feedback is investigated. But the authors focus on real-time control of optical systems.
Abstract: We investigate a control technique for spatially extended systems combining spatial filtering with a previously studied form of time-delay feedback. The scheme is naturally suited to real-time control of optical systems. We apply the control scheme to a model of a transversely extended semiconductor laser in which a desirable, coherent traveling-wave state exists, but is a member of a nowhere stable family. Our scheme stabilizes this state and directs the system towards it from realistic, distant, and noisy initial conditions. As confirmed by numerical simulation, a linear stability analysis about the controlled state accurately predicts when the scheme is successful and illustrates some key features of the control including the individual merit of, and interplay between, the spatial and temporal degrees of freedom in the control.
67 citations
TL;DR: The FLDI simulation software is shown to complement experiments by providing the necessary information to allow quantitative density fluctuation magnitudes to be extracted from experimental measurements.
Abstract: A computational method for predicting the output of a focused laser differential interferometer (FLDI) given an arbitrary density field is presented. The method is verified against analytical predictions and experimental data. The FLDI simulation software is applied to the problem of measuring Mack-mode wave packets in a hypervelocity boundary layer on a 5° half-angle cone. The software is shown to complement experiments by providing the necessary information to allow quantitative density fluctuation magnitudes to be extracted from experimental measurements.
67 citations