Abstract
The study of solitary wave solutions of nonlinear propagation equations is a fascinating topic of nonlinear dynamics. Analysis of their stability and nonlinear evolution properties is one of the most crucial parts in the problem of self- trapping of optical beams. Two-dimensional (stripe) beams, including solitary wave solutions, are unstable in bulk nonlinear media. The reason is that in bulk media these beams constitute a low- dimensional (1+1) subclass of higher-dimensional (2+1) allowable solutions and break up due to transverse instabilities along the “hidden” homogeneous coordinate. We present a spectrum of experimental and theoretical data demonstrating all stages of breakup and subsequent complex spatial evolution of stripe beams for both a focusing and defocusing photorefractive nonlinear response. The presented results include transverse modulation instability of a bright solitary stripe (Fig. 1) and snake instability of a dark stripe beam with subsequent formation of vortices or wave front defects (Fig. 2). The breakup of wide beams results in the generation of hundreds of (2+1) filaments (spatial turbulence, Fig. 3). Experiments with input speckle beams demonstrate the difference in the spatial statistics of the output field due to focusing or defocusing nonlinearities. The results given here for a photorefractive nonlinearity are generic to a broad class of nonlinear media. Nonetheless, we have observed some specific signatures of anisotropic spatial decay, that are discussed theoretically and experimentally.
© 1996 Optical Society of America
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