U. K. Krieger et al., JQSRT 89, 191 (2004)

We measure photon-counting histograms of single levitated micron-size droplets with a single solid inclusion. These histograms are compared with histograms obtained using a model of a nonconcentric sphere within a sphere. Based on this comparison we try to distinguish whether the solid inclusion is located at the surface of the host or is free to diffuse through its volume. The results show that a distinction between
both cases cannot be made definitively from a single photon-counting histogram alone, but this distinction becomes possible by evaluating numerous histograms with different ratios of the radius of the inclusion to that of the host. For a solid NaCl inclusion in an aqueous NaCl–MgCl2 solution we conclude it is free to diffuse throughout the volume of the liquid host.