Spatial self-action effects: self-bending and dark solitons

Abstract

The self-bending effect (i.e., the deflection of the trajectory of a laser beam in a third-order nonlinear material) is a fundamental phenomenon associated with the propagation of a beam with an asymmetrical intensity profile that forms a self-induced prism in a nonlinear refractive medium. This effect was predicted more than 20 years ago, and a few experimental pulsed-laser observations have been made. Recently we made the first cw observation and detailed measurement of self-bending by using sodium vapor and materials with a thermal nonlinearity (e.g., gasoline). We also used this effect for spectroscopic measurements of the nonlinear refractive index in sodium vapor and semiconductors (ZnSe) by measuring the self-deflection at various frequencies. Possible applications of self-bending include radiation protection and optical limiting, optical bistability and interconnecting, nonlinear coupling, and ultrafast beam scanning. Various incident-beam intensity profiles may result in other spatial self-action effects. In particular, by using these same materials and an amplitude grating (a wire mesh) as a mask for the incident beam, we made the first observation of spatial dark solitons. The formation of a stable grid of dark soliton stripes inside a nonlinear (defocusing) material and remarkably tightly organized nonlinear diffraction patterns in the far-field area behind the nonlinear sample were demonstrated. Our computer simulation and analytical calculations verified the soliton nature of the observed phenomena.