# Dual-Frequency Sub-Doppler Spectroscopy: Extended Theoretical Model and Microcell-Based Experiments

## TL;DR

This paper develops an extended theoretical model for dual-frequency sub-Doppler spectroscopy in Cs vapor cells, explaining experimental results and highlighting its potential for miniaturized optical frequency references.

## Contribution

The work introduces a comprehensive theoretical model that accounts for real atomic structures and nonlinear effects, advancing understanding of dual-frequency sub-Doppler spectroscopy.

## Key findings

- Quantitative agreement between theory and experiment.
- Identification of spatial oscillations in resonance amplitude.
- Potential for miniaturized high-performance optical references.

## Abstract

Doppler-free spectroscopy using two counter-propagating dual-frequency laser beams in alkali vapor cells has been demonstrated recently, providing the detection of high-contrast sign-reversed natural-linewidth sub-Doppler resonances. However, to date, only a qualitative theory based on a simplified $\Lambda$-scheme model has been reported to explain underlying physics of this phenomenon. In this work, we develop a general and extended theoretical model of dual-frequency sub-Doppler spectroscopy (DF SDS) for Cs D1 line. The latter considers the real atomic energy structure, main relaxation processes and various nonlinear effects including optical pumping, optical transition saturation, Zeeman and hyperfine coherent population trapping (CPT) states. This model allows to describe quantitatively the respective contributions of involved physical processes and consequently to estimate main properties (height and linewidth) of detected sub-Doppler resonances. Experimental results performed with a Cs vapor micro-fabricated cell are reported and explained by theoretical predictions. Spatial oscillations of the sub-Doppler resonance amplitude with translation of the reflection mirror are highlighted. Reported results show that DF SDS could be a promising approach for the development of a fully-miniaturized and high-performance optical frequency reference, with applications in various compact quantum devices.

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Source: https://tomesphere.com/paper/1812.09641