SPECKLE FROM A ROUGH-SURFACE WHEN THE ILLUMINATED REGION CONTAINS FEW CORRELATION AREAS - EFFECT OF CHANGING THE SURFACE HEIGHT VARIANCE

We report speckle contrast measurements taken at the centre of the far-field diffraction pattern of weak, medium and strong diffusers illuminated by a focused laser beam. We study the evolution of curves of speckle contrast as a function of the radius of the laser spot as the variance of surface height is steadily increased for a fixed correlation length. We also present experimental curves of speckle contrast as a function of the distance of the rough surface from the beam focus for three of the diffusers. © 1979.