Temporal behavior of backscattering instabilities in a three-dimensional cylindrical hot spot: II. Modified decay regime and user guide

The space and time behavior of backscattering instabilities in a three-dimensional cylindrical hot spot of finite lifetime is computed analytically in the modified decay regime. A uniform expression for the instantaneous backscattered power, valid for any time and any hot spot intensity in the modified decay regime, is proposed. It is shown that the finite transverse size of the hot spot leads to important diffraction effects that can significantly reduce the hot spot backscattered energy. A "user guide" is provided for an easy use of this model whatever the instantaneous regime of the instability: Standard decay, modified decay, and nonlinearly saturated (the hot spot depletion being taken into account heuristically). All the parameters needed in this model are given in physical units for both stimulated Brillouin scattering and stimulated Raman scattering.