Enhancement of radiation trapping for quasi-resonant scatterers at low temperature

TL;DR

This paper develops a transport equation for incoherent radiation in low-temperature quasi-resonant atomic gases, accounting for atomic motion, and solves it numerically to reveal differences from classical models.

Contribution

It introduces a generalized Bethe-Salpeter based transport equation that includes atomic motion effects and solves it with a novel Monte Carlo method.

Findings

Partial frequency redistribution affects emitted flux and energy density.

Long-time behavior of specific intensity differs from Holstein's prediction.

Numerical solutions show the impact of atomic motion on radiation transport.

Abstract

We present a transport equation for the incoherent propagation of radiation inside a quasi-resonant atomic gas at low temperature. The derivation is based on a generalized Bethe-Salpeter equation taking into account the motion of the atoms. The obtained equation is similar to the radiative transfer equation. It is solved numerically by an original Monte Carlo approach in the case of a slab geometry. The partial frequency redistribution caused by the small velocity of the scatterers make the emitted flux outside the system and the energy density inside the medium to behave differently than in the case of complete frequency redistribution. In particular, the long time dependence of the specific intensity (escape factor) is slightly different from the Holstein prediction.