A TIME-DEPENDENT BEAM-PROPAGATION METHOD TO MODEL PHOTOINDUCED EFFECTS IN GLASS

A numerical model for photoinduced second-harmonic generation in glass is presented. We use the beam-propagation method (BPM) to model the e ffects of focusing a laser beam and its second harmonic into a bulk sa mple of glass. The two-color optical field produces asymmetric photoio nization, and hence charge separation within the glass. We follow the evolution of the optical fields with the BPM, and compute the distribu tion of trapped charges in the glass using a directional photoionizati on source term. The model can predict the shape of the dc electric fie lds, the underlying charge distributions, and the modal patterns of th e generated second-harmonic light. We also include the time dependence of photoinduced nonlinear effects in glass. The mode patterns and dc field shapes agree with published experimental data, confirming the re sults of this simulation. ,