Diffusion Induced Modulational Interactions in Semiconductor Plasmas

Based on the hydrodynamic model of-plasmas an analytical investigation of frequency modulational interaction between co-propagating high frequency pump and electrostrictively generated acoustic mode is carried out in a semiconductor medium. The consequent steady-state amplification characteristics of the modulated waves are also reported. Using coupled mode theory, the effect of excess carriers diffusion on the threshold field and gain profile of the modulated wave is extensively studied. The origin of this interaction is assumed to lie in the induced non-linear diffusion current density of the medium. By considering the modulation process as a four-wave parametric interaction, an expression for effective cubic susceptibility describing the phenomenon is deduced. The modulation is greatly modified by propagation characteristics such as dispersion and diffraction due to dielectric relaxation of acoustic mode. The threshold pump field and steady-state growth rates are estimated from the effective cubic polarization in the plasma medium. Analytical estimation reveals that in the presence of enhanced diffusion due to excess charge carriers, the modulated beam can be effectively amplified in a dispersion-less acoustic wave regime. The moderately doped medium and low wavelength region are found to be most suitable for the onset of diffusion-induced modulational interaction in the medium.