PHOTON-CORRELATION SPECTROSCOPY ON FLOWING POLYDISPERSE FLUID-PARTICLE SYSTEMS - THEORY

We develop an analytical expression for the homodyne autocorrelation f unction of laser light scattered by a laminar flow of a polydisperse p article-fluid system. In contrast to the already existing literature o n the development of autocorrelation functions, we explicitly begin wi th the effects of the finite linewidth of the light source, the spatia l and temporal intensity averaging that is due to the detection proces s, the Brownian particle movement on the amplitudes of the scattered l ight waves as well as on the degree of resolution that we introduce in this paper, and a general system velocity v = (upsilon(x), upsilon(y) , upsilon(z)). One main result is a new physical interpretation of the well-known, generally empirically introduced coherence factor. Quanti ties that are comparable to the well-known degree of coherence, cohere nce area, and number of coherence areas have also been obtained. Final ly the investigations are simplified to an autocorrelation function th at can be used for the analysis of fluid-particle systems in the low K nudsen number regime. It is shown that in this case particle size or s ize distribution, system velocity, and particle concentration can be o btained simultaneously. The developed autocorrelation function is rela ted to frequently analyzed special cases and compared with expressions from the literature. (C) 1998 Optical Society of America.