Dependence on geometry of coherent Raman-scattered Stokes mode in weakly polar magnetized semiconductors

Using electromagnetic treatment, a detailed analytical investigation is made of the coherent Raman scattering (CRS) of the Stokes component of scattered wave in an obliquely magnetized (with respect to the direction of propagation) weakly polar III–V semiconductor. The origin of the CRS process lies in the third-order nonlinear optical susceptibility arising from the induced nonlinear current density (due to finiteness of Szigeti effective charge and differential polarizability) and interaction of pump wave with the density fluctuation generated within the medium. The agreement in magnitude of the third-order Raman susceptibility between our calculated values and experimental as well as other theoretical values is found to be good. Using the coupled mode theory of plasmas the steady-state Raman gain coefficient is determined via the effective susceptibility. The results suggest that magnetic field enhances the CRS gain coefficient by a factor of three when cyclotron frequency is tuned to optical phonon frequency under moderate pump field strengths. For field strengths E0>108 V m−1, the contribution of effective charge is nearly wiped off and the Raman gain spectrum becomes dependent on differential polarizability only. The CRS gain coefficient increases with increasing scattering angle and results in a maximum value for the backscattered mode. The backward Raman gain is found to be nearly 104 times larger than forward gain. The analysis also suggests the possibility of observing optical phase conjugation via CRS in weakly polar III–V semiconductors subjected to an external magnetic field.