Dynamic properties of three-dimensional speckles formed in free space on a diffuse object by an illuminating Gaussian beam have been investigated by evaluation of the space–time cross-correlation function. It has been found that the major axis of three-dimensional static speckles is always directed to the center of the beam spot on the object but that dynamic speckles are directed to a position other than the center according to the velocity of the object. Moreover, the motion of dynamic speckles is composed of two types: shifting and tilting.
© 1993 Optical Society of America
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