Spectral Fluctuations in the Stokes Output Pulse Pumped with a High-Pressure CO2 Laser

Analytical solution of the broadband Stokes field, whose linewidth is 2 GHz full width at half-maximum (FWHM), in four-wave mixing based upon stimulated Raman scattering is obtained using the fully quantum mechanical approach developed by Raymer et al. [Phys. Rev. A 32 (1985) 332]. Shot-to-shot variations of the Stokes energy initiated by quantum noise are calculated and the probability distribution function of the pulse energy is shown to be of negative-exponential shape in a no-pump-depletion region. Output Stokes field is expanded into the coherent modes, and it is shown that the most significantly excited mode of the Stokes field contains more than 99% of the Stokes pulse energy. Shot-to-shot fluctuations of the mean frequency of the narrow-band Stokes field, whose linewidth is 100 MHz (FWHM), is 200 MHz; however, that of the broad-band Stokes field reaches 1 GHz.