The coherent Raman scattering in astrophysics; application to a new   model of quasar
  The "Impulsive Stimulated Raman Scattering" (ISRS), is generally performed using ultrashort laser pulses. It shifts the frequency of the laser beam without any change of the wave surfaces and any appearance of extra lines. ISRS works with the pulses which make the usual incoherent light provided that the interactive medium is a low pressure gas having low frequency Raman transitions, that is an hyperfine spectrum. ISRS has no intensity threshold, but at low intensity level it becomes a linear effect, so that the relative frequency shift $\Delta\nu/\nu$ is nearly constant in the spectrum. This linear effect named "Incoherent Light, Coherent Raman Scattering" (ILCRS) may be confused with a Doppler effect in astrophysics; it explains all optical properties of the quasars, including the debatable ones, in particular the width of the BAL lines, the infrared thermal radiation attributed to hot dust, and the spectral discrepancies attributed to a variation of the hyperfine constant. 
Jacques Moret-Bailly