Quantum theory of Stokes generation with a multimode laser

The quantum theory of Stokes generation by stimulated Raman scattering of a multimode laser is developed and analyzed. For large laser-mode spacing, the generated Stokes intensity is found to be independent of the number of laser modes for both high and low gains. The result applies to both free-running and mode-locked lasers and is in contrast to that in the Raman amplifier, in which gain is found to depend on the number of modes. The Stokes light is generated with mode amplitudes and phases in perfect correlation with those of the laser. Also, in steady state the instantaneous Stokes intensity is found to follow exactly the rapid fluctuations of the laser intensity.