Spatially resolved and spatial-frequency domain reflectance of bounded media in low-scattering regimes.

We investigate the impact of bounded turbid media in the low-turbidity regime on spatially resolved and spatial frequency domain reflectance. In this regime, dominated by single scattering, reflectance becomes highly sensitive to the scattering phase function, offering insights that are typically averaged out in highly diffuse media. Using aqueous suspensions of polystyrene microspheres with varying sizes confined in glass cuvettes, we observe distinct, geometry-dependent optical phenomena: a pronounced double-peak structure in the spatially resolved and clear oscillations in spatial frequency domain reflectance. Monte Carlo simulations confirm that these features arise from single scattering events coupled with internal reflections at the sample boundaries. By combining orthogonal and oblique illumination and detection geometries, our approach effectively samples the scattering phase function at two distinct supplementary angles. This methodology provides a powerful framework for the noninvasive characterization of particle size distributions in dilute suspensions and offers a highly sensitive metric for the precise characterization of reflectance measurement setups.