Speckle from a rough surface when the illuminated region contains few correlation areas: The effect of changing the surface height variance

Abstract

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.