The dynamic behaviour of laser speckle caused by uniform in-plane motion of a diffuse object has been studied by deriving the cross-correlation functions of the complex disturbance and the intensity in a field where the speckle is observed. The expressions for the diffraction and the image fields are calculated from general formulae for a linear coherent system. On the basis of these functions two characters in the dynamic behaviour of speckle, a bodily translation and a gradual change in structure, are discussed quantitatively. The velocity of the translation and the rate of the structure change have been derived. As applications of the relations obtained several new methods have been proposed for measuring pattern correlations, MTF of imaging systems, in-plane velocity of diffuse objects, and eye accommodation state.
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