Active phase and polarization locking of a 1.4 kW fiber amplifier

A three-stage Yb-fiber amplifier emitted 1.43 kW of single-mode power when seeded with a 25 GHz line width master oscillator ( MO). The amplified output was polarization stabilized and phase locked using active heterodyne phase control. A low-power sample of the output beam was coherently combined to a second fiber amplifier with 90% visibility. The measured combining efficiency agreed with estimated decoherence effects from fiber nonlinearity, linewidth, and phase-locking accuracy. This is the highest-power fiber laser that has been coherently locked using any method that allows brightness scaling. (C) 2010 Optical Society of America