Doppler-free spectroscopy on Cs D$_1$ line with a dual-frequency laser

TL;DR

This paper demonstrates Doppler-free spectroscopy on Cs D1 line using a dual-frequency laser, revealing a sign-reversal of absorption dips due to CPT effects and achieving highly stable laser frequency locking.

Contribution

It introduces a dual-frequency laser approach for Doppler-free spectroscopy that enhances absorption signals and improves laser frequency stability compared to traditional methods.

Findings

Sign-reversal of saturated absorption dips observed

Enhanced Doppler-free atomic absorption achieved

Laser frequency stability improved by an order of magnitude

Abstract

We report on Doppler-free laser spectroscopy in a Cs vapor cell using a dual-frequency laser system tuned on the Cs D$_1$ line. Using counter-propagating beams with crossed linear polarizations, an original sign-reversal of the usual saturated absorption dip and large increase in Doppler-free atomic absorption is observed. This phenomenon is explained by coherent population trapping (CPT) effects. The impact of laser intensity and light polarization on absorption profiles is reported in both single-frequency and dual-frequency regimes. In the latter, frequency stabilization of two diode lasers was performed, yielding a beat-note fractional frequency stability at the level of $3 \times 10^{-12}$ at 1 s averaging time. These performances are about an order of magnitude better than those obtained using a conventional single-frequency saturated absorption scheme.