Diffuse photon remission associated with the center-illuminated-area-detection geometry. III. Perspectives on the patterns of saturation

Understanding scattering-insensitiveness in diffuse reflectance spectroscopy (DRS) will be useful to enhance the spectral specificity to absorption. In DRS based on center-illuminated-area-detection (CIAD), the scattering response can saturate as the relative strength of scattering with respect to the collection-size, represented by a dimensionless reduced scattering, increases over a threshold. However, the formation of saturation versus the same range of dimensionless reduced scattering may differ between a fixed reduced-scattering over an increasing collection-size (case 1) and an increasing reduced scattering over a fixed collection-size (case 2), due to the absorption. Part III demonstrates the differences of the scattering saturation as well as the effect of absorption on it in the CIAD geometry between the two cases while assessed over the same range of the dimensionless reduced scattering. A model allows predicting the absorption-dependent levels of saturation and the corner parameters of saturation transition. When assessed for the absorption coefficient to vary over [0.001, 0.01, 0.1, 1] mm-1, the model-predicted levels of saturation agree with MC results with ≤2.2% error in both cases. In comparison, the model-predicted corner parameters of saturation show much different agreements with MC results in the two cases, suggesting that the saturation pattern is much better formed in one than in the other. Experiments conforming to the CIAD geometry support the discrepancy of the saturating patterns between the two cases.