Influence of a buffer gas on nonlinear magneto-optical polarization rotation

We show experimentally that the presence of a buffer gas in a rubidium vapor cell modifies significantly the nonlinear magneto-optical rotation of polarization of near-resonant light propagating through the cell. We observe not only the well-known narrowing of the nonlinear magneto-optical resonances, but also changes in their shape and visibility. We explain these effects in terms of coherence-preserving, velocity-changing collisions between rubidium and buffer gas atoms.