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 ($lambd
a ~= ~852 nm)$ 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.
Experimental and theoretical studies are presented related to the ground-state magneto-optical resonance prepared in Cesium vapour confined in an Extremely Thin Cell (ETC, with thickness equal to the wavelength of the irradiating light). It is shown
that the utilization of the ETC allows one to examine the formation of a magneto-optical resonance on the individual hyperfine transitions, thus distinguishing processes resulting in dark (reduced absorption) or bright (enhanced absorption) resonance formation. We report on an experimental evidence of the bright magneto-optical resonance sign reversal in Cs atoms confined in the ETC. A theoretical model is proposed based on the optical Bloch equations that involves the elastic interaction processes of atoms in the ETC with its walls resulting in depolarization of the Cs excited state which is polarized by the exciting radiation. This depolarization leads to the sign reversal of the bright resonance. Using the proposed model, the magneto-optical resonance amplitude and width as a function of laser power are calculated and compared with the experimental ones. The numerical results are in good agreement with the experiment.
