Demonstration of a 1 Joule, 500 W average power picosecond laser

We report the demonstration of a chirped pulse amplification laser system that produces 1.5 J pulses at 0.5 kHz repetition rate and 0.75 kW average power. These pulses are subsequently compressed resulting 1 J, similar to 5 ps duration pulses at 500 Hz repetition rate. The 8-pass main amplifier consists of two diode-pumped, cryogenic-temperature Yb: YAG active mirrors cooled by a thermally efficient, high capacity cryogenic-cooling system. This amplifier operates with an optical-to-optical efficiency of 37%. The amplified pulses have excellent beam quality with a measured M-2 factor of similar to 1.3. Over 30 minutes of continuous operation, we measured a shot-to-shot pulse energy fluctuation of only 0.75% RMS over the nearly 1 million shots fired. This laser was employed to make the first demonstration of a compact, plasma-based EUV/soft x-ray laser operating at a repletion rate of 400 Hz. In this proof-of-principle demonstration, shaped 1 J pulses of picosecond duration were focused onto a rotating molybdenum target at grazing incidence. The resulting plasma is collisionally ionized to the Ni-like ionic stage where a large, transient population inversion results in production of bright lambda = 18.9 nm laser pulses.