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| Main Authors: | , |
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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2601.00173 |
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Table of Contents:
- We study first-return statistics for photons undergoing three-dimensional Henyey-Greenstein scattering in a semi-infinite medium. In previous work, we showed that one-dimensional first-passage probabilities can be expanded using Catalan and Motzkin generating functions. Extending this framework to three dimensions requires introducing a Boundary Truncation Factor (BTF), which accounts for the restricted angular phase space imposed by the boundary. Extensive Monte Carlo simulations are used to determine the BTF empirically as a function of scattering order and anisotropy. For moderate anisotropy, the BTF is accurately described by a Cauchy kernel, with parameters depending only on the Henyey-Greenstein asymmetry factor. This closed-form expression reproduces Monte Carlo results with 1-2% accuracy over a broad range of scattering orders. At higher anisotropy, systematic deviations from the Cauchy form are observed. These deviations can be reduced using a one-parameter generalized kernel. We further extend the framework to oblique incidence by replacing the normal-incidence return probability with a Legendre-series formulation. The BTF parameters and Motzkin counting machinery remain independent of the incidence angle, so only the anchor point of the algorithm changes. The resulting framework provides a computationally efficient mapping from three-dimensional anisotropic transport at arbitrary incidence to one-dimensional combinatorial first-passage theory.