Dispersion of bound electron nonlinear refraction in solids

A two-hand model is used to calculate the scaling and spectrum of the nondegenerate nonlinear absorption. From this, the bound electronic nonlinear refractive index n₂ is obtained using a Kramers-Kronig transformation. The authors include the effects of two-photon and Raman transitions and the AC Stark shift (virtual band blocking). The theoretical calculation for n₂ shows excellent agreement with measured values for a five-order-of-magnitude variation in the modulus of n₂ in semiconductors and wide-gap optical solids. Beam distortion methods were used to measure n₂ in semiconductors. The observations result in a comprehensive theory that allows a prediction of n₂ at wavelengths beneath the band edge, given only the bandgap energy and the linear index of refraction. Some consequences for all-optical switching are discussed, and a wavelength criterion for the observation of switching is derived