Nonlinear optics in anisotropic media

Abstract

Nonlinear electromagnetic propagation in materials having anisotropic nonlinear susceptibilities induces complex dynamical phenomena which can be controlled by appropriate engineering of the material. Two optical examples are studied, of second-harmonic generation and third-order polarisation instabilities in cubic semiconductors, exemplified by gallium arsenide. Crystalline materials, including semiconductors, can exhibit highly anisotropic nonlinear suscepti- bility tensors, on account of the point group of symmetries of the crystal lattice. Symmetries in the bulk crystal lattice can be reduced by the application of external fields such as strain or magnetic fields, and also by fabrication of the material in quantum-well or superlattice form, leading to the possibility of externally controllable birefringence and nonlinear anisotropy. Electromagnetic waves propagating in such complex media exhibit varied nonlinear dynamical behaviour which can take place on femtosecond time scales, with very great potential for ultrafast switching and signal processing devices. These devices may operate over any part of the electromagnetic spectrum, from microwaves to optical frequencies. Understanding the range of effects which might be exploited in this way leads to new physical and mathematical problems in electromagnetic theory.