Characterization of random media by low-coherence interferometry

We describe the use of low-coherence interferometry (LCI) for the structura l characterization of nonuniform media with mesoscopic heterogeneities. The high sensitivity of LCI to the phase properties of scattered light makes i t a suitable technique for the direct determination of size, concentration, and uniformity of heterogeneities in multi-phase systems. To demonstrate t his, we examine using LCI to study a range of polystyrene microsphere suspe nsions with particle sizes ranging from 41 to 818 nm and concentrations fro m 0.25% to 10% by weight. The particle size and concentration information w as extracted from the amplitude of the signal by using the theory of light scattering in nonuniform media. We have shown that the fluctuations in the unaveraged LCI signal may be utilized to extract additional information abo ut system uniformity.