Simultaneous Occurrence of and Competition between Stimulated Optical-Scattering Processes in Gases

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Abstract
Using the gain coefficients for individually stimulated Brillouin and Raman transitions in gases, we have been able to predict the pressure and temperature at which the gain coefficients for various transitions are equal. The competition between simultaneously stimulated optical-scattering processes has been studied in the vicinity of these predicted intersections. Within a limited range of parameters, two processes can be stimulated simultaneously. The experimentally observed gain for the weaker process is affected by the presence of the intense Stokes beam associated with the dominant process in some instances, but not in others. Using idealized models, the enhancement of the gain coefficients due to the presence of additional intense-frequency components and the reduction of gain due to depletion of laser power have been considered, but neither effect yields a consistent explanation of the observed behavior. The competition between vibrational Raman-vibrational Raman, vibrational Raman-rotational Raman, Raman-Brillouin, and forward-reverse propagating Raman were studied. In all of these experiments, no evidence for enhancement of gain, but several examples of reduction in gain, were observed.