Two Dimensional Spatial Solitons with Second-Order Nonlinearities

In addition to harmonic generation and frequency-mixing, intense light beams propagating in χ(2) nonlinear media exhibit a variety of self- and cross-phase modulation effects which until recently were commonly thought to occur only in χ(3) interactions. One important example is the propagation of soliton-like waves, in which the fundamental and second-harmonic waves mutually focus and trap each other. The (1+1) trapping (i.e. one transverse dimension and one propagation dimension) yields both spatial and temporal solitons that can in principle occur in planar waveguides and fibers, respectively [1]-[2] Although spatial solitons appear to be easier to obtain experimentally than temporal solitons, their excitation still requires nearly phase-matched propagation in high quality planar waveguides. In this paper we report our investigations on the propagation of Gaussian beams in bulk χ(2) media [3]. Contrarily to the conventional self focusing case in bulk Kerr like media, we show that stable 2D-soliton like propagation is possible, in the paraxial, in phase matchable materials with a quadratic nonlinear response. Under a variety of currently available experimental conditions, in the presence of finite mismatch and linear walk-off between the fundamental and second harmonic waves, we predict the experimental observation of such new physical processes.