Abstract

The stability of wave propagation has always been a major concern in nonlinear optics. The breakup of an intense monochromatic beam in a Kerr-type self-focusing medium was among the first nonlinear optical effects observed and is well-understood for third order nonlinear materials[1]. In geometries with two transverse dimensions, the nonlinear Schrodinger leads to catastrophic self-focusing (blow-up instability). Furthermore, one-dimensional solutions, when used in a geometry with two transverse dimensions, will also be subject to a large class of perturbations which lead to instabilities. Recently new origins for self-focusing effects have been observed in media with quadratic nonlinearities involving the strong coupling between a fundamental (FW) and a second harmonic (SH) beam.[2] The spatial instability properties of such a coupled two-beam system have not yet been investigated to date. Here we report a combined experimental and theoretical investigation of this phenomenon for quasi-one-dimensional beam inputs in a quadratic medium, KTP, near its phase-matching condition for second harmonic generation (SHG).

© 1996 Optical Society of America