Spatial distribution of two symmetric four-wave mixing signals induced by Gaussian beams

TL;DR

This paper provides a theoretical analysis of the spatial profiles of symmetric four-wave mixing signals in a two-level atomic medium, highlighting effects of incident power and spectral properties on their propagation.

Contribution

It introduces a comprehensive model accounting for spatial and spectral dependencies of nonlinear susceptibilities in four-wave mixing with Gaussian beams.

Findings

Total incident power influences transverse signal profiles.

Spectral characteristics affect longitudinal propagation.

Asymmetries arise from different detunings of incident fields.

Abstract

We present a theoretical analysis of the spatial shape of two symmetric signals of degenerate four-wave mixing induced by Gaussian beams in a thin sample of two-level atoms. Our calculations take into account the full spatial and spectral dependencies of the relevant nonlinear susceptibilities that govern the two processes. This reveals two interesting effects. The first one is that the total power of incident beams affects the transverse profile of the four-wave mixing signals at the medium exit and their free propagation. The second one is the influence of the spectral characteristics of the medium on the longitudinal profile of both generated signals upon free propagation. We argue that the first effect can be seen as the saturation of the medium in regions of higher intensity, while the second can be understood as the result of a nonlinear contribution to the refractive index inside the atomic medium. These effects can be symmetric between the two signals, with asymmetries induced by different detunings from resonance of the incident fields.