Abstract

A rigorous theory of the teraherz field generation in semiconductors by and its interaction with a femtosecond (fs) optical field is presented for a (3+1)-dimensional case. Quasiadiabatic following approximation combined with the band-structure representation of the semiconductor is utilized to determine a set of coupled equations for the optical and teraherz fields. For the teraherz wave a generalized Kadomtsev-Petviashvili equation is found: it is coupled to a nonlinear Schrödinger equation governing the dynamics of the optical field. This asymptotic regime is valid away from classical slowly varying envelope approximation (SVEA), rotating-wave approximation or classical anharmonic oscillator resonance. Analytic solutions are given that (i) resemble solutions to coupled cross-phase-modulation equations usually obtained for two co-propagating optical fields, and (ii) show how the temporal structure of the fs optical pulse affects the spatial structure of the teraherz field. It is shown that the diffraction of the teraherz field displays temporal dispersive effects, which could barely be observed if treated within the SVEA Experimentally measurable quantities to detect these new observations are discussed.

© 1998 IEEE