Laws of laser speckle movement and their application in flow visualization

Yaozu Song; Wei-Bao Zhang

doi:10.1117/12.365729

13 October 1999 Laws of laser speckle movement and their application in flow visualization

Yaozu Song, Wei-Bao Zhang

Proceedings Volume 3783, Optical Diagnostics for Fluids/Heat/Combustion and Photomechanics for Solids; (1999) https://doi.org/10.1117/12.365729
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

In this paper a mathematical model for a laws of laser speckle movement in space when light beam pass through a phase object is proposed by using the Fresnel-Kirchhoff diffraction integral. By means of the theoretical analysis for this mathematical model, the following three conclusions can be got. First, when a light beam passes through a phase object, for example a transparent flow fluid, the movement state of speckles in space depends not only on the characteristic function on surface of speckle sources, but also on infinitely small variation of propagation direction of incident beam. If the characteristic function can be kept same during a double exposure, then the movement states of speckle in space and their corresponding speckle displacements depend only on the variation of propagation direction of incident beam. Second, to make the characteristic function same during a double exposure the considered light beams which produce a pair of correlation speckles must come from the same space zone on the surface of speckle source. Third, when a light beam passes through a diffusion surface, the variation of propagation direction of the beam can not be determined by the principle of geometrical optics because of scatting function of light beams on diffusion surface. But the principle of geometrical optics still can be used in discussion of the movement states of speckle in space and in determination of speckle displacements according to the mathematical model proposed in this paper. Above these analysis provides a theoretical basis for designing experimental arrangements of laser speckle photography in flow visualization. According to the laws of laser speckle movement in space six different experimental arrangements which can be used in flow visualization are presented. The formulas of processing the experimental data for measurement density field and temperature field in flow fluid are given. These results are very favorable for development of laser speckle photography technology in flow visualization.

Citation Download Citation

Yaozu Song and Wei-Bao Zhang "Laws of laser speckle movement and their application in flow visualization", Proc. SPIE 3783, Optical Diagnostics for Fluids/Heat/Combustion and Photomechanics for Solids, (13 October 1999); https://doi.org/10.1117/12.365729

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