An investigation of laser speckle using a linear, charge-coupled, photodiode array : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physics at Massey University

Abstract

This thesis describes the use of a linear, charge-coupled, photodiode array, and microprocessor in the measurement of various laser speckle statistics. Contrast and probability densities for fully and partially developed speckle patterns are derived theoretically as a function of scattering angle and surface roughness. The experimental apparatus incorporating the photodiode array and microprocessor is described in detail, along with various experiments to check expected specifications. Using this apparatus, measurements are made of the probability density and contrast, as a function of scattering angle, for the speckle patterns produced by three different surfaces. From these results and the theoretical predictions the roughness parameters for these surfaces are determined. In-plane surface displacement is measured using a cross-correlation technique and is found to produce accurate results over a wide range of displacements (from lµm to 0.5mm). A short section on speckle size is also included to verify theoretical predictions made in an earlier chapter.