We describe the use of low-coherence interferometry (LCI) for the structural characterization of nonuniform media with mesoscopic heterogeneities. The high sensitivity of LCI to the phase properties of scattered light makes it a suitable technique for the direct determination of size, concentration, and uniformity of heterogeneities in multi-phase systems. To demonstrate this, we examine using LCI to study a range of polystyrene microsphere suspensions with particle sizes ranging from 41 to 818 nm and concentrations from 0.25% to 10% by weight. The particle size and concentration information was 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 about system uniformity.
S. R. Thurber, A. M. Brodsky, and L. W. Burgess, "Characterization of Random Media by Low-Coherence Interferometry," Appl. Spectrosc. 54, 1506-1514 (2000)