INTERACTION BETWEEN OPTICAL-FREQUENCY AND TERAHERTZ-FREQUENCY FIELDS IN CHI((3)) MATERIALS

Asymptotic evolution equations are derived to describe the interaction between an optical field and a terahertz-frequency field copropagatin g in a chi((3)) material. Second-order and fourth-order multiple-scale perturbation theory is utilized to derive a set of coupled equations for the optical and the terahertz fields. For the terahertz wave a mod ified Korteweg-de Vries equation is found; it is coupled to a nonlinea r Schrodinger equation describing the dynamics of the optical field. T his asymptotic regime is valid away from classical natural-oscillator- frequency or quantum-mechanical-transition resonances. Analytic soluti ons to the evolution equations are given that resemble solutions to co upled cross-phase-modulation equations usually obtained for two coprop agating optical fields. The long- to short-wavelength resonance equati ons have distinctive features that enable the optical fields to respon d to the low-frequency fields. Experimentally measurable quantities to detect these interactions are discussed. (C) 1997 Optical Society of America.