The excitation of additional waves caused by a spatial dispersion transforms the stimulated Raman and Brillouin scattering in the vicinity of the excitonic resonance into a kind of a four-wave mixing. The parametric coupling of four exciton polariton waves (EPW's) on the nonlinear polarization caused by the nonlinear polariton-phonon interaction results in the amplification of the Stokes additional wave. The Raman and Brillouin gain coefficients of the Stokes waves depending on the amplitudes and the wave vectors of both pumping EPW's essentially differ from the ones in the case without additional waves. The nonlinear Raman or Brillouin polarization containing additional waves generates a spectrum of scattered harmonics which consists of 20 harmonics with the combination wave vectors and frequencies instead of one anti-Stokes wave and one wave with the frequency lower than the Stokes frequency in the case without additional waves. The results obtained show that stimulated light scattering can be an effective method for the experimental investigation of additional waves and additional boundary conditions due to the amplification of additional waves. [References: 24]
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