A version of a scheme of speckle intefferometry is considered, which is intended for the analysis of the distribution of refractive-index gradients in optically transparent media. The application of this approach to problems of hydrodynamics and gas dynamics makes it possible to determine the structure of the distribution of optical inhomogeneities in liquid and gaseous flows. The method is based on the recording of patterns of two speckle structures obtained in the plane of spatial frequencies by using illumination with an auxiliary speckle structure. One speckle structure is formed in the absence of an object, and the other one is formed by transilluminating an object. In comparison with other known phase methods, the speckle-interferometry methods make it possible to change the measurement sensitivity in a wide range and substantially simplify the interpretation of the results obtained.
A version of a scheme of speckle interferometry is considered, which is intended for the analysis of the stationary distribution pattern of steep refractive-index gradients in optically transparent media. The application of this approach to problems of hydrodynamics and gas dynamics allows one to determine the structure of distribution of optical inhomogeneities in liquid and gaseous flows or media. The method is based on the recording of patterns of two speckle structures obtained in the plane of image formation of the object by an optical system when the object is illuminated by radiation having an auxiliary speckle structure. The patterns correspond to the two positions of an object shifted somewhat in the direction of the optical axis of the system. Contrary to the common methods of speckle interferometry, only the state of the object being investigated for two different conditions of illumination by the probe radiation is used for the detection in this case. The difficulties arising in the measurements of the objects with steep refractiveindex gradients by the known methods of speckle interferometry are accordingly practically eliminated in the scheme under consideration. In comparison with the schlieren phase methods, this method offers higher possibilities in the variation of sensitivity.
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