SELF-LENSING IN SODIUM VAPOR - INFLUENCE OF SATURATION, ATOMIC DIFFUSION AND RADIATION TRAPPING

Beam shaping processes, such as self-lensing, strongly influence many experiments in nonlinear optics. Concentrating on the self-defocusing case, we present a detailed experimental and theoretical investigation of the lens-like behavior of an atomic vapor optically pumped by a Ga ussian laser beam and discuss the validity of a description of the vap or as a thin, ''ideal'' lens. Through comparison between experimental results and theoretical predictions, we show how the simultaneous pres ence of ''local'' effects (saturation) and ''nonlocal'' effects (atomi c and radiation diffusion) contribute to the radial distribution of th e index of refraction in the vapor. The separate contributions of atom ic and radiation diffusion are experimentally identified by measuremen ts with different buffer gases. A good qualitative agreement between t he experimental results and the theoretical predictions is obtained, a lthough hyperfine and propagation effects are neglected. (C) 1998 Else vier Science B.V.