Temporal dynamics of Levy flights of photons in a hot vapor

TL;DR

This study investigates the Levy flight behavior of photons in hot vapor, demonstrating that the Levy parameter can be extracted from backward fluorescence and is consistent across different measurement methods, revealing insights into scattering processes.

Contribution

First measurement of the Levy parameter from time-resolved backward fluorescence in hot vapor, confirming its consistency with forward measurements and theoretical models.

Findings

Levy parameter α ≈ 1 for both forward and backward photons.

Backward photons exhibit some single scattering events even at high density.

Results align with theoretical simulations of photon scattering in vapor.

Abstract

Multiple scattering of light by resonant vapor is characterized by Levy-type superdiffusion with a step size distribution $P(x) \propto 1/x^{1+{\alpha}}$, with $0 < {\alpha} < 2$. The Levy parameter ${\alpha}$ was measured from $P(x)$, steady fluorescence, frequency-dependent fluorescence and time-resolved transmission, all of them in the forward direction. Here we report first measurements of this quantity from timeresolved backward fluorescence, i.e., photons that are backward diffused from light pulses exciting a hot rubidium vapor. We show experimentally that ${\alpha}$ can be extracted from this diffuse reflection, and the results are consistent with time-resolved transmission (i.e., photons that are forward diffused) and steady frequency-dependent forward fluorescence. Theoretical simulations are consistent with these results. We also show that, although we measure ${\alpha} = 1$ for both transmission and reflection, the backward photons have a non-negligible amount of single scattering events even for high density, contrary to the forward photons where multiple scattering dominates.