Measuring the group velocity dispersion in near resonant hot atomic vapors

TL;DR

This paper presents a novel, simple method to measure group velocity dispersion in near-resonant hot atomic vapors using phase modulation and a photodetector, overcoming limitations of traditional techniques.

Contribution

It introduces a new technique based on modulation contrast oscillations to directly measure GVD in hot atomic vapors, avoiding complex pulse or interferometric methods.

Findings

Demonstrated the method on hot rubidium vapors across the D2 line

Observed strong frequency dependence of GVD over a broad detuning range

Provided a practical approach for accurate GVD measurement in resonant atomic media

Abstract

Group velocity dispersion (GVD) in near-resonant hot atomic vapors is difficult to measure with standard pulse broadening or interferometric techniques, as absorption, pulse distortion and nonlinearities strongly affect the probe and reduce the signal-to-noise ratio. We introduce a simpler method using a continuous-wave laser with weak phase modulation and a slow photodetector, directly inspired by Bragg-like spectroscopy in fluids of light. During propagation, the red and blue-detuned sidebands accumulate different dispersive phase shifts, leading to oscillations in the transmitted modulation contrast as the modulation frequency is scanned. Vanishing contrast at well-defined frequencies directly yields the GVD. We apply this technique to hot rubidium vapors and observe the strong frequency dependence of the GVD across a broad detuning range of the D2 line at different temperatures.