Brillouin-induced wave mixing using cw signals

Abstract

High performance forms of Brillouin mediated two-wave mixing [stimulated Brillouin scattering (SBS) amplification] and four-wave mixing [Brillouin enhanced four-wave mixing (BEFWM)] are documented to be sensitive to quite low energy, i.e., picojoule level, pulsed signals. These thresholds are small enough to be exceeded by the energy delivered by a laser diode pumped cw Nd:YAG laser during the several nanoseconds in which the pulsed pump radiation is present in the nonlinear medium. We have observed, we believe for the first time, SBS amplification and BEFWM phase conjugation of cw signals using pulsed pumping with enhancements that agree well with those obtained using low energy pulsed signals. The cw input eliminates the precise pump-signal synchronization required when all inputs are pulsed. Heterodyne mixing of the cw input with the cw injection seeding beam of the pulsed pump laser yields precise knowledge and control of the nearly degenerate input frequency relationships without using SBS frequency shifting. Resonance spectra of BEFWM and SBS amplification as a function of geometry recorded in these improved experimental conditions reveal detunings that do not appear to be entirely accounted for by standard Brillouin scattering theory.