We report the observation of transverse optical bistability (TOB) in a sodium-filled Fabry-Pérot resonator, pumped by circularly polarized light, nearly resonant with the ${\mathit{D}}_1$ line, in the presence of a buffer gas, for low vapor density. A sequence of circularly symmetric patterns, ascribable to superpositions of resonator modes, is obtained. The appearance of TOB can be explained in terms of a self-induced intensity-dependent lens formed in the medium by the interaction with the laser light. A simple model that considers the transverse diffusion of the atoms inside the cell provides predictions in good qualitative agreement with the observations.

• Received 30 December 1991

DOI:https://doi.org/10.1103/PhysRevA.45.R4237