A speckle pattern is a random interference pattern which is formed when a highly coherent beam is scattered from a rough surface. As the beam scans across the surface the speckle pattern changes in time giving rise to random fluctuations in the current of a photodetector which collects the scattered light. This phenomenom is called speckle noise, and is of great importance in laser scanning devices such as barcode readers. The purpose of this talk is to present the mathematical model of Gaussian speckle patterns, and to explain how the theory of random processes can be used in studying spectral properties of speckle noise. In particular, we will show how an application of the Wiener-Khinchine theorem yields the distribution of the noise power in the frequency domain. We shall also discuss the signal-to-noise ratio (SNR) when the scanning beam moves across a surface of nonuniform reflectance. We will derive estimates for the lower bound of SNR for some simple reflectance functions, and explain the implications of this to laser barcode scanning.

Collaborators: Prof. E. Marom, Tel Aviv University and Prof. L. Bergstein, Brooklyn Politechnic.