Phase noise suppression for a high-power optical frequency comb

We demonstrate a high-power frequency comb consisting of a Ti:sapphire bulk seed laser and a large-mode-area Yb-fiber power amplifier. An all-fiber pulse stretcher was carefully designed to suppress the amplitude-to-phase noise in the fiber amplifier. Near-Fourier-limited pulses were obtained with an average power of up to 30 W and a pulse duration of 178 fs. The free-running carrier-envelope-phase frequency was optimized to have a linewidth of 52 kHz, which was further phase-locked to a narrow linewidth of 1.8 mHz with an integrated phase noise of 0.78 rad.