Effect of stimulated raman scattering on the formation of the random lasing spectrum of dyes

The nature of the line structure of the random lasing spectrum of vesicular films activated by dyes (rhodamine 6G, pyrromethene 597) has been analyzed. The spectral lines appear above the random lasing threshold and are manifested only within the spectrum of the amplified spontaneous radiation of dye molecules against the continuous-pedestal background. Their intensities are proportional to the product of the intensities of the pump and continuous spectrum at the frequencies of these lines, and the frequencies are exactly reproduced from pulse to pulse. The shifts of the lines are strongly correlated with the pump frequency and the frequencies of these lines coincide with the frequencies of the Raman scattering lines of dye molecules. Using these properties, it has been shown that the observed lines are due to stimulated resonant Raman scattering by dye molecules, which occurs simultaneously with the stimulated emission of these molecules. These two processes affect each other and jointly form a united nonlinear process where all of the oscillations active in Raman scattering are manifested.