Dynamics of second-harmonic generation in a photovoltaic photorefractive quadratic medium

We investigate second-harmonic generation (SHG) in a photorefractive photovoltaic medium such as lithium niobate. Our numerical model reveals the complex dynamics of the parametric process during the buildup of the index modification due to the photorefractive (PR) nonlinearity. We investigate a condition in which no external field is applied to the crystal, resulting in a defocusing nonlinearity, as well as the case in which an external bias is applied, producing a self-focusing effect that can enhance the conversion efficiency of the parametric process. We also find the conditions for the initial phase matching and for the background illumination leading to a stable self-confined propagation of the second-harmonic generated light. The developed numerical model shows that as a general case SHG in a self-focusing PR medium results in mode beating inside the generated waveguide, as experimentally observed. (C) 2009 Optical Society of America