A 1.4-kW Mode-Controllable Fiber Laser System

We demonstrated a mode-controllable fiber laser system with output power of 1.4 kW level. The system consists of a kilowatt-scale master oscillator power amplifier and an active feedback control system based on the stochastic parallel-gradient descent algorithm. We can convert the LP
₀₁
and LP
₁₁
modes by performing an extremum search for power in the bucket of the output beam. Under the same pump power, we obtain the mode conversion of LP
₁₁
to LP
₀₁
, and the efficiency is as high as 99.5%. The maximum output power of LP
₁₁
and LP
₀₁
mode are 1396 W and 1389 W, respectively, with corresponding slope efficiencies of 85.8% and 84.1%.