Raman scattering by polaritons under nonstationary conditions. II: Local and wave nonstationary cases

Abstract

AbstractThe theoretical investigation of stimulated Raman scattering (RS) by polaritons under nonstationary conditions, when local or wave nonstationary properties are separately important has been carried out on the basis of a fluctuation‐dissipation method. General experssions are found which describe the scattered radiation (Stokes and polariton) nonstationary angular distribution at the piezo‐electric crystal scattering layer exit face. In particular, for the local nonstationary case, the detailed analysis of the cases of small stationary gain and of very short and moderately short pump pulses at large stationary gain is carried through. For small stationary gain and also in the case of very short pulses with arbitrary gain, the spontaneous RS regime is realized, the Stokes wave intensity time dependence being on the whole a purely parametric one. The delay effects connected with the finite nature of the scattering polaritons' relaxation time become significant when the coherent component of the polaritons is important. Typical numerical calculations of the scattered radiation pulse shape and peak intensity are carried out for pump pulses of the rectangular and domed form. The most important general manifestations of nonstationary properties of the polariton RS are the apperance of deformation, asymmetry and delay of the scattered radiation pulses relative to the pump pulses; the angular tuning of the pump duration and the scattered radiation frequency tuning; the different character of the influence of local and wave nonstationary properties and so on. These effects are determined by shape and duration of the pump pulses and also by the stationary gain parameter in the material and by the scattering polaritons' relaxation time (for the local nonstationary case) or by the group delay time of the Stokes wave relatively to the pump wave (for the wave nonstationary case).