PARAMETRIC DISPERSION AND AMPLIFICATION OF ACOUSTOHELICON WAVES IN PIEZOELECTRIC SEMICONDUCTORS

Assuming that the origin of the nonlinear interaction lies in the second-order optical susceptibility arising from the nonlinear induced current density and using the coupled-mode theory, the parametric dispersion and amplification of acoustohelicon waves is analytically investigated in a longitudinally magnetized piezoelectric semiconductor of noncentrosymmetric nature. The relevant experiments have not been reported. The threshold value of the pump electric field E(O)th and its corresponding excitation intensity is obtained. The longitudinal magnetic field decreases the required magnitude of E(O)th for the excitation of parametric amplification. The phenomenon of self-defocusing of the signal in the prevailing case is found to be a consequence of the negative dispersive characteristics exhibited by the acoustohelicon waves. Numerical analyses are performed for an InSb crystal at 77 K, duly irradiated by frequency-doubled pulsed 10.6-mu-m CO2 lasers. The parametric gain constant is observed to be maximum when the cyclotron frequency omega-(c) attains the magnitude equal to that of omega-(o), the incident laser frequency ( = 1.78 x 10(14) s-1).