We present an experimental study of laser-induced continuum structure in cesium, performed by observing the birefringence and dichroism induced in the atomic medium by a circularly polarized laser embedding the 8s ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$ state into the ionization continuum. The optimization of the sensitivity for the detection of the polarization rotation has allowed a high-accuracy measurement of the resonance profile. A quantitative comparison with theoretical predictions, taking into account the hyperfine structure of atomic levels, shows a clear evidence of a line-broadening effect due to cesium resonant collisions.

• Received 14 September 1992

DOI:https://doi.org/10.1103/PhysRevA.47.4219