Diffuse photon remission associated with the center-illuminated-area-detection geometry. II. Approach to the time-domain model

This part proposes a model of time-dependent diffuse photon remission for the center-illuminated-area-detection (CIAD) geometry, by virtue of area integration of the radially resolved time-dependent diffuse photon remission formulated with the master-slave dual-source scheme demonstrated in Part I for steady-state measurements. The time-domain model is assessed against Monte Carlo (MC) simulations limiting to only the Heyney-Greenstein scattering phase function for CIAD of physical scales and medium properties relevant to single-fiber reflectance (SfR) and over a 2 ns duration, in compliance with the timespan of the only experimental report of SfR demon-strated with a 50 mu m gradient index fiber. The time-domain model-MC assessments are carried out for an absorption coefficient ranging three orders of magnitude over [0.001, 0.01, 0.1, 1] mm-1 at a fixed scattering, and a reduced scattering coefficient ranging three orders of magnitude over [0.01, 0.1, 1, 10] mm-1 at a fixed absorption, among others. Photons of shorter and longer propagation times, relative to the diameter of the area of collection, respond differently to the scattering and absorption changes. Limited comparisons of MC between CIAD and a top-hat geometry as the idealization of SfR reveal that the time-domain photon remissions of the two geometries differ appreciably in only the early arriving photons. (c) 2023 Optica Publishing Group

Automated summary

This part introduces a time-dependent diffuse photon remission model for CIAD geometry, formulated through area integration of radially resolved time-dependent diffuse photon remission. The model is assessed against Monte Carlo simulations and limited to Heyney-Greenstein scattering phase function for relevant physical scales and medium properties of SfR. The assessments are carried out for various absorption and reduced scattering coefficients, and show differences in the response of photons with shorter and longer propagation times.