Lateral beam splitting in sodium vapour: magneto-optical origin and polarization competition effects

An almost linearly polarized laser beam focused into a sodium vapour cell m ay split into spatially separated components of opposite circular polarizat ion. The symmetry of the emerging structures is controlled by static magnet ic fields of the order of the Earth's field. The mechanism of the decomposi tion of the light field into its two spin components is clarified by numeri cal simulations revealing the evolution of the spatial distribution of the light field during the propagation through the sodium vapour. In this conte xt, the experimentally observed occurrence of a negative differential power transmission can be explained.