Power locking of high-repetition-rate chirped pulse amplifiers

We report a feedback control scheme that minimizes the energy fluctuations of high power femtosecond pulses from a 1 kHz laser amplifier. The pulse energy variation in the frequency bandwidth 0-500 Hz was obtained by a photodiode and a low pass filter. The measured signal was fed to a proportional-integral-derivative (differential) (PID) controller that changed the amplitude of the high voltage pulses applied to a Pockels cell. The variation of average power was reduced from 1.33% RMS to 0.28% RMS, which improved the carrier-envelope phase stability from 500 mrad to 200 mrad as measured by two f-to-2f interferometers. The long term stability of the laser was kept to approximately 0.5% RMS.