Saturation effects in the sub-Doppler spectroscopy of Cesium vapor confined in an Extremely Thin Cell

TL;DR

This study explores how saturation effects influence absorption and fluorescence spectra of Cesium vapor in an Extremely Thin Cell, revealing different behaviors at specific cell thicknesses and providing experimental and theoretical insights into sub-Doppler phenomena.

Contribution

It presents new experimental observations and theoretical analysis of saturation effects in sub-Doppler spectroscopy of Cesium in an Extremely Thin Cell at specific thicknesses.

Findings

Dicke-narrowed absorption broadens and saturates with intensity at L=λ/2

Sub-Doppler dips appear at L=λ due to saturation and optical pumping

Experimental results align with two-level model calculations

Abstract

Saturation effects affecting absorption and fluorescence spectra of an atomic vapor confined in an Extremely Thin Cell (cell thickness $L < 1 \mu m$) are investigated experimentally and theoretically. The study is performed on the $D_{2}$ line ($\lambda ~= ~852 nm)$ of $Cs$ and concentrates on the two situations $L = \lambda /2$ and $L =\lambda$, the most contrasted ones with respect to the length dependence of the coherent Dicke narrowing. For $L = \lambda /2$, the Dicke-narrowed absorption profile simply broadens and saturates in amplitude when increasing the light intensity, while for $L =\lambda$, sub-Doppler dips of reduced absorption at line-center appear on the broad absorption profile. For a fluorescence detection at $L =\lambda$, saturation induces narrow dips, but only for hyperfine components undergoing a population loss through optical pumping. These experimental results are interpreted with the help of the various existing models, and are compared with numerical calculations based upon a two-level modelling that considers both a closed and an open system.