Coherent Backscattering with Nonlinear Atomic Scatterers

TL;DR

This paper investigates how nonlinear inelastic two-photon scattering in cold atomic gases affects coherent backscattering, revealing that nonlinear effects can enhance the backscattering signal beyond linear limits when using frequency filtering.

Contribution

It introduces a perturbative analysis of nonlinear effects in coherent backscattering, showing interference of three amplitudes and enhancement of backscattering beyond the linear barrier.

Findings

Nonlinear inelastic scattering contributes to coherent backscattering.

Frequency filtering enhances nonlinear backscattering signals.

Backscattering enhancement factor exceeds two with nonlinear effects.

Abstract

We study coherent backscattering of a quasi-monochromatic laser by a dilute gas of cold two-level atoms. We consider the perturbative regime of weak intensities, where nonlinear effects arise from {\em inelastic} two-photon scattering processes. Here, coherent backscattering can be formed by interference between {\em three} different scattering amplitudes. Consequently, if elastically scattered photons are filtered out from the photodetection signal by means of suitable frequency-selective detection, we find the nonlinear backscattering enhancement factor to exceed the linear barrier two.