Full stabilization of eight-channel Yb-fiber coherent beam combining system delivering 1.18-kW, 1.18-mJ, 270-fs pulses

We develop an ultrafast Yb-fiber laser system based on eight-channel coherent beam combining utilizing commercially available rod-type Yb-fibers. To ensure good combining efficiency and long-term operation of the system at the attosecond laser facility under construction, we fully stabilize the phase, group-delay, and beam-pointing of the eight fiber channels. Especially, we propose a novel multi-step hill climbing method to control both group-delay and beam-pointing. At a repetition rate of 1 MHz, this laser system delivers 270-fs pulses with 1.18-kW average power (1.18-mJ pulse energy). The average-power instability of the laser system running for 12 hours is 0.32%.