Non-linear magneto-optical polarization rotation in dark and bright coherent states

摘要

We have measured non-linear Faraday effects for dark and bright long-lived Zeeman coherences in the D2 resonance line of ~(85)Rb, for linearly polarized input laser light. Zeeman coherence in the bright state show enhanced nonlinear effects, larger values for the angle of polarization rotation and higher rates of the polarization rotation, similar to recent results for higher refractive index and dispersion in the bright state of Cs. Dark and bright states also show different dependence of both polarization rotation angle and of polarization rate on the laser intensity, while the resonance width for both states varies similarly with the laser intensity. We show small enhancement of such non-linear effects when the laser beam diameter increases from 1 mm to 5 mm. Ellipticity of transmitted laser beam vary strongly for amplitudes of the external magnetic field smaller then 50 mG, but the maximum value of the ellipticity remains below π/300.