Large Faraday rotation of resonant light in a cold atomic cloud

We experimentally studied the Faraday rotation of resonant light in an optically thick cloud of laser-cooled rubidium atoms. Measurements yield a large Verdet constant in the range of ${10}^5$°/T mm and a maximal polarization rotation of 150°. A complete analysis of the polarization state of the transmitted light was necessary to account for the role of the probe laser’s spectrum.