Interference and nonlinear properties of four-wave-mixing resonances in thermal vapor: Analytical results and experimental verification

TL;DR

This paper presents an analytical model for four-wave mixing in thermal rubidium vapor, incorporating hyperfine and Doppler effects, validated by experiments, and explains the nonlinear optical resonances at room temperature.

Contribution

The paper introduces an analytical approach to model four-wave mixing resonances in thermal vapors, including hyperfine and Doppler effects, with experimental verification and high accuracy.

Findings

Model accurately predicts resonance positions and shapes.

Excellent agreement between theory and experiment at low intensities.

Analytical expressions relate nonlinear susceptibility to Voigt profiles.

Abstract

We develop a model to calculate nonlinear polarization in a nondegenerate four-wave mixing in diamond configuration which includes the effects of hyperfine structure and Doppler broadening. We verify the model against the experiment with $5^{2}S_{1/2}$, $5^{2}P_{3/2}$, $5^{2}D_{3/2}$ and $5^{2}P_{1/2}$ levels of rubidium 85. Treating the multilevel atomic system as a combination of many four-level systems we are able to express the nonlinear susceptibility of a thermal ensemble in a low-intensity regime in terms of Voigt-type profiles and obtain an excellent conformity of theory and experiment within this complex system. The agreement is also satisfactory at high intensity and the analytical model correctly predicts the positions and shapes of resonances. Our results elucidate the physics of coherent interaction of light with atoms involving higher excited levels in vapors at room temperature, which is used in an increasing range of applications.