Coherent Brillouin scattering in noncentrosymmetric semiconductors: bound and free charge carriers contribution

Abstract

With the aid of a hydrodynamic model for semiconductor plasmas, an analytical investigation of coherent Brillouin scattering (CBS) has been made in noncentrosymmetric (NCS) semiconductor plasmas both under the presence and in the absence of an externally applied magnetic field. Using the coupled mode approach, the nonlinear induced polarization and third-order nonlinear optical susceptibility, due to bound and free charge carrier nonlinearity, are obtained. The analysis further deals with the qualitative behavior of the threshold pump electric field E T for onset of CBS and the resulting gain coefficient (steady-state as well as transient, [g B]SS,TR) in NCS semiconductor plasmas. Numerical estimates are made for InSb crystal at 77 K duly irradiated by a pulsed 10.6 μm CO2 laser. The effects of piezoelectricity, doping concentration and magnetic field on both the E T and [g B]SS,TR have been studied in detail. E T required for onset of the CBS process is found to be lower when piezoelectricity is present and the doping level of the semiconductor is moderate than in other conditions. It is found that when the magnetic field is applied, the coherent backward Stokes wave can be amplified by a factor of 10² in NCS semiconducting crystals. The analysis also suggests the idea of pulse compression and the possibility of observing the phase conjugation reflection coefficient ∼106 which proves its potential for the fabrication of CBS-based phase conjugate mirrors.