  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.
