Polarization-ellipse rotation by induced gyrotropy in atomic vapors

We study theoretically and experimentally a new mechanism for the rotation of the polarization ellipse of a single laser beam propagating through an atomic vapor with a frequency tuned near an atomic resonance. The results of a theoretical treatment for the case of a J = (1/2) to J = (1/2) atomic transition show that a rotation of the polarization ellipse of the laser beam will occur as a result of ground-state optical pumping and that the angle of rotation is independent of the laser intensity over a broad range of laser intensities. The predictions of this theoretical model are tested experimentally through the use of potassium vapor and are found to agree with the experimental data.