Introduction

Abstract

The random intensity distribution that we now call a speckle pattern (see Fig. 1.1) is formed when fairly coherent light is either reflected from a rough surface or propagates through a medium with random refractive index fluctuations. Such patterns are clearly visible even to the casual observer when highly coherent laser light is used. In general the statistical properties of speckle patterns depend both on the coherence of the incident light and the detailed properties of the random surface or medium, although for perfectly coherent light this dependence on the random scatterer is almost negligible if the scatterer introduces path differences greater than one wavelength. Although we are concerned here with the random speckle patterns produced when visible coherent light is scattered, it should be emphasized that closely related phenomena arise in other regions of the electromagnetic spectrum and also for particles; typical examples are the scattering of X-rays by liquids, radar ‘clutter’ and electron scattering by amorphous carbon films.