Dual-wavelength-pumped Tm^3+-doped ZBLAN fiber MOPA at 813  nm

We report a dual-wavelength-pumped (1220 nm + 1050 nm) Tm^3+-doped ZBLAN fiber master oscillator power amplifier (MOPA) system at 813 nm for the lattice laser of the Sr optical lattice clock (OLC). Since the photodarkening effect of the Tm^3+-doped fiber is more serious in the 800 nm region, it was suppressed by applying real-time photobleaching with a 532 nm laser for obtaining stable output. We also investigated the dependence of conversion efficiency on the launched pump power ratio (P_1220 nm/P_1220+1050 nm) and found that the maximum conversion efficiency of 50% was obtained from the pump power ratio of 41%. By installing real-time photobleaching and dual-wavelength pumping, our MOPA system generated the maximum output power of 1.95 W with slope efficiency of 48%, which is the highest output power at around 810 nm from fiber laser sources, to the best of our knowledge.