Low coherence reflectometry of randomly inhomogeneous media: basic approaches to data processing

Various approaches to interpretation of the low-coherence reflectometry (LCR) data obtained using LCR probes of fine- and coarse-grained random media are discussed. Depending on the relationship between the sample thickness and the transport mean free path of light propagation in the sample, different methods of data analysis must be used. In the case of thin strongly scattering samples, the transport mean free path can be recovered using estimation of the average decay rate of the scan-depth-dependent LCR signal. On the contrary, this technique is not applicable in the case of thick multiple scattering media. Under this condition, the transport mean free path can be obtained using comparison of the scan-integrated reflectometric signal for the used detection conditions with the reference data obtained using Monte-Carlo simulation of light propagation in the probed sample. In turn, the obtained transport mean free path characterizes the structure of the examined sample (i.e., the average size of cells in highly porous or foam-like samples). The considered approaches are illustrated by the results of LCR probing of strongly scattering composite materials, foamy liquids, and highly porous polymer matrices (scaffold prototypes).