Fluorescence Seeding of Stimulated Raman Scattering in Microdroplets

Simulated Raman scattering (SRS), in the absence of external seeding, builds up from spontaneous Raman noise. When the pump-laser pulsewidth is much longer than the dephasing time of the vibrational relaxation, the SRS spectrum is dominated by the vibrational mode with the maximum Raman gain. The depletion of the input-laser intensity by the SRS-buildup of the Raman mode with the largest gain prevents the SRS-buildup of other Raman modes with weaker gain. Selective feedback in a two-mirror resonator geometry was used to enhance the growth of SRS of the weaker 801 cm1 mode of cyclohexane in an optical cell by lowering the feedback for the strong 2929 cm–1 mode. In a Raman gain experiment, a Raman amplifier is used to amplify a weak seeding beam generated by a Raman oscillator or a tunable laser.