Topic
Speckle imaging
About: Speckle imaging is a research topic. Over the lifetime, 3730 publications have been published within this topic receiving 62354 citations.
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14 Jun 1995
TL;DR: In this paper, the effect of speckle integration implicit in digitization by pixels of finite size is considered using computer-generated specckle patterns, and it is shown that the phase errors decrease monotonically with decreasing speckles diameter.
Abstract: Phase measurements using digital speckle pattern interferometry are subject to random errors due to speckle decorrelation and electronic noise. A phasor description of speckle decorrelation is introduced from which the r.m.s. phase error is calculated. Phase noise due to additive Gaussian errors on the phase-stepped images is shown to be statistically equivalent to that from decorrelation, allowing the r.m.s. phase error from electronic noise to be obtained analytically. The currently used noise reduction strategy of speckle averaging is shown to be optimal in that it provides the maximum likelihood estimate of speckle phase change. Finally, the effect of speckle integration implicit in digitization by pixels of finite size is considered using computer-generated speckle patterns. It is shown that the phase errors decrease monotonically with decreasing speckle diameter.
29 citations
TL;DR: The algorithm uses the fast Fourier transform to diagonalize and decouple the system of equations which results from the application of the least-squares criterion and is accurate and stable, and is perhaps an order of magnitude faster than the best iterative method.
Abstract: This paper describes a fast direct algorithm for obtaining least-squares phase estimates from arrays of noisy phase differences. The algorithm uses the fast Fourier transform to diagonalize and decouple the system of equations which results from the application of the least-squares criterion. It is accurate and stable, and is perhaps an order of magnitude faster than the best iterative method. The effectiveness of the algorithm has been demonstrated by using it in connection with the Knox–Thompson speckle-imaging procedure to restore an optical object perturbed by simulated atmospheric turbulence. Representative results are discussed in the paper.
29 citations
TL;DR: In this paper, a laser shearography instrument that utilizes coherent imaging fiber bundles to port four spatially multiplexed speckle images to a single CCD camera via a shearing Michelson interferometer is presented.
Abstract: Shearography is a full-field interferometric speckle technique used to determine displacement derivatives. Measurement of surface strain is possible using shearography if six components of displacement gradient are calculated. This can be achieved using shearography instrumentation that incorporates at least three measurement channels combined with two orthogonal shear directions. This paper presents a laser shearography instrument that utilizes coherent imaging fibre bundles to port four spatially multiplexed speckle images to a single CCD camera via a shearing Michelson interferometer. The four images are spatially multiplexed onto the sensor of a CCD camera. Wrapped phase maps are derived from the recorded speckle interferograms using temporal phase stepping. The unwrapped phase maps are combined with the measurement channel sensitivity vectors using a matrix operation to determine the required displacement derivatives. Results from an out-of-plane displacement of a flat aluminium plate are presented and compared with a computational model. Results from a second test object that show in-plane and out-of-plane strain components are also shown.
29 citations
TL;DR: It is revealed that the complete randomness of the speckle phase can play the role of a standard phase in a statistical sense, and the phase of the object under testing can be derived in a Statistical way, in contrast to conventional interferometry.
Abstract: A new technique of optical interferometry based on the statistics of the fully developed speckle field is proposed. It is revealed that the complete randomness of the speckle phase can play the role of a standard phase in a statistical sense, and the phase of the object under testing can be derived in a statistical way, in contrast to conventional interferometry. The technique is first described in relation to the phase-shifting interferometry and the compensation problem for the phase-shift error. Next the method is generalized as an independent interferometric technique.
29 citations
TL;DR: In this article, a fly-eye-like imaging system for detecting objects embedded in scattering media is presented, where objects are recovered from many speckled images observed by a digital camera through a microlens array.
Abstract: A fly-eye-like imaging system for seeing objects embedded in scattering media. Objects are recovered from many speckled images observed by a digital camera through a microlens array. Each microlens in the array generates a speckle image of the object buried between two layers of chick breast tissue. In the computer, each image is Fourier transformed jointly with an image of the speckled pointlike source captured under the same conditions. A set of the squared magnitudes of the Fourier-transformed pictures is accumulated to form a single average picture. This final picture is again Fourier transformed, resulting in the reconstruction of the hidden object.
28 citations