Speckle imaging

About: Speckle imaging is a research topic. Over the lifetime, 3730 publications have been published within this topic receiving 62354 citations.

Optically phase-locked electronic speckle pattern interferometer.

Abstract: The design, theory, operation, and characteristics of an optically phase-locked electronic speckle pattern interferometer (OPL-ESPI) are described. The OPL-ESPI system couples an optical phase-locked loop with an ESPI system to generate real-time equal Doppler speckle contours of moving objects from unstable sensor platforms. In addition, the optical phase-locked loop provides the basis for a new ESPI video signal processing technique which incorporates local oscillator phase shifting coupled with video sequential frame subtraction.

Deformation analysis with temporal speckle pattern interferometry

Abstract: The continual deformation of an object will lead to a temporal speckle pattern. By analyzing this time-dependent speckle pattern the temporal deformations of the object can be obtained. We propose a method for measuring the displacement components caused by defor- mations using the temporal speckle pattern interferometry (TSPI). By capturing a series of speckle interference patterns related to the object deformations, we can get the fluctuations in the intensity of the interfer- ence patterns. Further, the phase maps for whole-field object displace- ments are calculated with the inversion of the temporal interference in- tensities by estimating both the average intensity and the modulation. In this way, one can quantitatively measure temporal displacements simply using a conventional electronic speckle pattern interferometry (ESPI) system without phase shifting or a carrier. An elaboration of the TSPI is presented and out-of-plane displacements caused by pressure and ther- mal deformations are measured. © 2001 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1336527)

Quantitative single-shot imaging of complex objects using phase retrieval with a designed periphery

Abstract: Measuring transmission and optical thickness of an object with a single intensity recording is desired in many fields of imaging research. One possibility to achieve this is to employ phase retrieval algorithms. We propose a method to significantly improve the performance of such algorithms in optical imaging. The method relies on introducing a specially designed phase object into the specimen plane during the image recording, which serves as a constraint in the subsequent phase retrieval algorithm. This leads to faster algorithm convergence and improved final accuracy. Quantitative imaging can be performed by a single recording of the resulting diffraction pattern in the camera plane, without using lenses or other optical elements. The method allows effective suppression of the “twin-image”, an artefact that appears when holograms are read out. Results from numerical simulations and experiments confirm a high accuracy which can be comparable to that of phase-stepping interferometry.

Remarkable algebraic structures of phase-closure imaging and their algorithmic implications in aperture synthesis

Abstract: To reveal some new results of a study concerning phase-closure imaging, first we introduce three key operators: the cophasing operator A, the phase-aberration operator B, and the phase-closure operator C. We then show that the generalized inverses of these operators are equal to their (Hilbert space) adjoints divided by the number of pupil pinholes. This remarkable property, which can be stated in terms of backprojection, plays an essential part in the understanding and the treatment of the inverse problems of aperture synthesis. The notion of backprojection is illustrated in a geometrical manner. As an example of applications we present a new self-calibration algorithm for solving the phase-restoration problem in radio imaging. The solution of this deconvolution problem is obtained without phase unwrapping by means of backprojection mechanisms. The implications of these structures in speckle imaging are also examined. Whenever possible, nonredundant configurations should be preferred. The main developments of our approach concern, in particular, the very-long-baseline array and the interferometric mode of the very large telescope.