2ND-ORDER AND 4TH-ORDER STATISTICS OF DOUBLY SCATTERED SPECKLE

The statistics of doubly scattered laser speckle, in which the size of the diffracting aperture is arbitrary relative to the spatial scales of the incident random field and the random diffuser in the aperture, is studied. The diffracted amplitude of the combined speckle and diffuser fields (both of which are spatially stationary) is shown to be non-stationary. A further spatial averaging can be carried out to yield an intensity correlation function termed the asymptotically stationary intensity correlation function) which depends upon a single spatial variable and thus possesses a power spectrum. Numerical calculations are carried out for representative situations, and their physical interpretation are discussed.