Dynamic Stark shift in a Doppler-broadened four-wave mixing

TL;DR

This paper provides a theoretical and experimental study of the AC Stark shift in four-wave mixing within a Doppler-broadened three-level system, highlighting the shift's dependence on laser parameters and system broadening.

Contribution

It introduces a detailed density matrix model for analyzing the Stark shift in Doppler-broadened four-wave mixing and validates it with experimental data in rubidium vapor.

Findings

AC Stark shift observed in nonlinear signal when scanning laser frequency

Good agreement between theoretical model and experimental results

Signal amplitude varies with laser power in predictable manner

Abstract

This work presents a theoretical analysis of the Autler-Townes splitting pattern in the four-wave mixing signal generated in a three-level cascade Doppler-broadened system. We employ the density matrix formalism to write the Bloch equations and solve them numerically. The solutions allow us to compare the response of the upper level population and the generated signal coherence for homogeneously and non-homogeneously broadened systems. Our results reveal an AC Stark shift in the nonlinear signal when the frequency of the strong or weak beam is scanned, in contrast to what is observed in the fluorescence. Furthermore, we present experimental data for the four-wave mixing signal in a hot rubidium vapor for the copropagating configuration of the exciting beams. The behavior of the AC Stark displacement and signal amplitude as a function of laser power indicates a good agreement between the model and the experimental results.