120 W subnanosecond ytterbium-doped double clad fiber amplifier and its application in supercontinuum generation

We report a 120 W high average power all-fiber subnanosecond master oscillator power amplifier (MOPA) system with a two-stage amplifier chain. The seed source is an ytterbium-doped single mode fiber laser passively mode-locked by nonlinear polarization rotation (NPR). Its pulse width is tunable from 0.59 ns to 1.2 ns by changing the length of the laser cavity. The average output power of 91.5 mW is obtained at 26.3 MHz with pulse width of 0.59 ns. A large mode area double cladding high-absorption ytterbium-doped fiber is introduced into the master power amplifier to suppress the nonlinear effects. Finally, 120 W average output power is obtained with single pulse energy of 4.56 μJ, and its optical-to-optical conversion efficiency is up to 83.9%. In addition, we demonstrate 19.5 W average-power supercontinuum generation in photonic crystal fiber (PCF) using this subnanosecond pulsed fiber amplifier.