Two symmetric four-wave mixing signals generated in a medium with anomalous refractive index

TL;DR

This paper presents experimental and theoretical analysis of two symmetric four-wave mixing signals in rubidium vapor, highlighting the importance of coherent effects like electromagnetically induced absorption for accurate spectral predictions.

Contribution

It introduces a comprehensive model that accounts for propagation and coherent effects to accurately describe symmetric four-wave mixing signals in rubidium vapor.

Findings

Two symmetric four-wave mixing signals are generated and detected in rubidium vapor.

A small frequency separation between peaks is observed and explained by propagation effects.

Including electromagnetically induced absorption is essential for accurate spectral modeling.

Abstract

We report experimental and theoretical results of two symmetrical signals of degenerate four-wave mixing generated in rubidium vapor. Both nonlinear signals are induced by two almost copropagating laser beams, with $\vec{k}_{a}$ and $\vec{k}_{b}$ wave-vectors, and detected simultaneously in the $2\vec{k}_{a}-\vec{k}_{b}$ and $2\vec{k}_{b}-\vec{k}_{a}$ directions. In each direction, we observe a single peak when the two beams are tuned on the closed transition $^{85}$Rb$~5S_{1/2} (F=3) \rightarrow 5P_{3/2} (F=4)$. The excitation spectra reveal a small frequency separation between the two peaks, which is explained when propagation effects are taken into account. Furthermore, our theoretical analysis shows that a correct description of the frequency position of each peak is obtained only if coherent effects such as electromagnetically induced absorption are included.