Continuous wave stimulated brillouin scattering in optical fibers: New results and applications for high power lasers

In this paper we review of our recent results in different aspects of fundamentals and applications of continuous wave (CW) stimulated Brillouin scattering (SBS) in optical fibers. We show that with increasing pump strength the temporally stable component emerges from initially stochastic Stokes emission slightly above the SBS threshold to become the dominant contribution at higher pump powers. The effect is independent of fiber characteristics. These findings are shown to be a manifestation of spectral self-phase conjugation in SBS providing first experimental evidence of this phenomenon in optics. In application domain a considerable power scaling for the MOPA system comprising a CW Nd:YAG master oscillator, a quasi-CW diode pumped Nd:YAG slab power amplifier and a fiber based SBS phase conjugate mirror is reported. A twelve-pass amplifier configuration is employed to achieve high gain in a small length slab amplifier. Residual and pump induced optical inhomogenities in the slab are corrected by the fibre phase conjugator to achieve diffraction limited output beam quality. 300 W quasi-CW output power and a maximal attainable gain of ~150 for the system are obtained. We also considered theoretically SBS in high power fiber amplifiers. We show that for an end-pumped rare-earth doped double-clad fiber the inhomogeneous distribution of temperature, which is caused by absorption of pump radiation, may result in total suppression of SBS even for output powers of CW single-frequency radiation well above 1000 W.