ROLE OF STIMULATED 4-PHOTON MIXING AND EFFICIENT STOKES GENERATION OF STIMULATED RAMAN-SCATTERING IN EXCIMER-LASER-PUMPED UV MULTIMODE FIBERS

Efficient frequency downconversion by stimulated Raman scattering (SRS) was obtained in a XeF excimer-laser-pumped fused-silica multimode fiber at 351 nm. Twenty orders of Stokes generation were observed covering a spectral range of approximately 8800 cm-1, a number we were able to predict numerically using a model for SRS only but incuding a finite gain width. Gains from stimulated four-photon mixing were found to be not important in SRS Stokes generation. Only occasionally did we observe new frequency lines in addition to the normal Raman lines, which are attributed to phase-matched wave mixing processes.