High-sensitivity study of laser-induced birefringence and dichroism in the ionization continuum of cesium

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{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.