Low-coherence interferometry of particles distributed in a dielectric medium

Low-coherence interferometry is used to measure changes in signal intensity that are dependent on the phase of the light backscattered fi om particles distributed in dielectric matrices. The measurements provide the unique opportunity to follow the dynamics of the small fraction of scattered light, to 10(-10) of the initial intensity, that retains phase characteristics of the incident wave packet. The wave phase effects are manifested in the observed reshaping of backscattered wave packets, the optical-length-dependent degree of phase randomization, and the fluctuation patterns. The experimental results indicate the presence of photon trapping effects. The corresponding data analysis not only allows for an estimation of particle concentration but also provides information on Brownian motion of particles in a liquid and characteristics of par-tide distribution in size and space. (C) 1997 Optical Society of America.