Measurements of extreme first passage times in photon transport

TL;DR

This paper experimentally measures the extreme first passage times of photons in scattering media, revealing significant deviations from traditional diffusion and telegraph models, and suggests a new understanding of photon transport in random environments.

Contribution

It introduces experimental measurements of EFPTs in photon transport, demonstrating their divergence from existing models and proposing a new perspective based on index-averaged medium traversal.

Findings

EFPTs differ from diffusion and telegraph predictions

Measured EFPTs align with traversal time in index-averaged medium

Results challenge the assumptions of traditional photon transport models

Abstract

Photon transport through turbid media has typically been modeled through diffusion or telegraph equations. These models describe behavior of the average, or typical, photon with remarkable accuracy, however, we show here that they fail to capture the Extreme First Passage Times (EFPTs) of photon transport. By sending ultra-fast bursts of photons through a scattering medium and timing the arrival of the first passage photon, we measure the distribution of these EFPTs of photons in a random environment. Our measured EFPTs differ from those predicted by both the diffusion approximation and telegraph equation. Instead, we observe the EFPT as the time expected for light to travel through an index-averaged medium. These results reveal flaws in both models and invite a re-examining of their underlying assumptions.