Theory of anisotropy of two-photon absorption in zinc-blende semiconductors

Two-photon absorption (2PA) in semiconductors is of interest as it provides a nonlinear spectroscopic technique in addition to having important consequences for all-optical switching. Earlier calculations and measurements of 2PA in zinc-blende semiconductors have concentrated on the linearly polarised single-beam case, that is ignoring any polarisation dependence. This polarisation dependence can take two forms. First, there is a dependence on the type of optical polarisation employed that in the single beam case gives a difference between linearly and circularly polarised light. This variation can occur even for isotropic media. Second, there is a variation in the 2PA coefficient depending on the relative orientation of the optical polarisation with the crystalline axes which will be the main topic of this paper