Stimulated-Brillouin-scattering-suppressed high-power single-frequency polarization-maintaining Raman fiber amplifier with longitudinally varied strain for laser guide star

An up to 44 W, 1 MHz linewidth, 1178 nm CW laser is obtained by Raman amplification of a distributed feedback diode laser in a variably strained polarization-maintaining fiber with a record-high optical efficiency of 52%, pumped by a linearly polarized 1120 nm fiber laser. A polarization extinction ratio of 30 dB is achieved due to the all-polarization-maintaining configuration and the polarization dependence of Raman gain. The strain distribution is designed according to the signal power evolution along the fiber. A 20 times reduction in the effective stimulated Brillouin scattering coefficient is achieved. A 24.3 W 589 nm laser is generated by an external resonant doubling cavity with an optical efficiency of 68.5%. The laser is locked to 589.1591 nm for a laser guide star.