Abstract

The intensity of thermal light varies randomly. A short exposure image produced by thermal light will therefore exhibit speckle, i.e. it will have bright regions corresponding to high intensity and dark regions corresponding to low intensity. A coherent image of an object whose surface is rough on the scale of the optical wavelength (true for most objects) will have speckle patterns. The intensity at each point on the image is a combination of contributions scattered from different points on the object's surface, making the intensity random and producing speckle. The expected area of these speckle regions is calculated in this study. For the purposes of calculating its area, a speckle region is defined as an excursion area of intensity over a given threshold value. The statistical analysis involves the concepts of two dimensional levels crossings and the statistics and spatial spectral properties of the intensity. The analysis is general and estimates the area of each excursion region for any gamma distributed two dimensional random process. Applications discussed include coherent imaging, conventional imaging, and damage areas on laser illuminated materials.

© 1990 Optical Society of America