Observation of ground-state Zeeman coherences in the selective reflection from cesium vapor

We report an observation of Δm=2 ground-state coherences in selective-reflection spectra at a glass–metal-vapor interface. The coherence was created by a linearly polarized laser beam tuned to a sub-Doppler resonance in the selective-reflection spectrum of the cesium ${\mathit{D}}_2$ line and detected through the magnetorotation of the plane of polarization of the reflected beam. The coherence effect appears as a dispersive shaped resonance of subnatural width. The dependence of the width on the intensity of the optical field shows a saturation behavior. For vanishing light intensity and cesium vapor pressure the linewidth is limited by transverse time-of-flight broadening, whereas its pressure dependence indicates an additional contribution from the finite longitudinal interaction time.