Low threshold SBS phase conjugation for quasi-cw laser systems

Summary form only. Phase conjugating mirrors (PCM) based on stimulated Brillouin scattering (SBS) are used to improve the beam quality of solid state lasers. Standard SBS mirror geometry in which the laser beam is focused into the SBS material exhibits peak power thresholds in the range of several 10 kW up to several 100 kW depending on the SBS material. Due to this high thresholds these mirrors can only be used with pulsed laser systems. To compensate phase distortions of cw-pumped or quasi-cw lasers new SBS-PCMs have to be developed. In addition to a low threshold in the range of 1 W, these PCMs shall have a large dynamic range, a high reflectivity and low coherence demands, too. For solving these problems we developed a phase conjugating mirror based on SBS in an internally tapered waveguide. This concept of the internally tapered waveguide combines low SBS thresholds with large dynamic power ranges. Using fused silica as the waveguide material peak power thresholds below 500W were measured.