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Cryogenically cooled, 149 W, Q-switched, Yb:LiYF4 laser.

We demonstrate a 149 W Yb:LiYF(4) laser with diffraction-limited beam quality at 995 nm. The laser, Q-switched at 10 kHz pulse repetition frequency, produces linearly polarized 52 ns pulses with a slope efficiency of 73%. The combination of cryogenic cooling and a low (3.5%) quantum defect results in minimal thermo-optic effects and high thermal efficiency. The measured heat load to the cryogen is 0.15 W per watt of output. These results show the potential for significant power scaling of Q-switched Yb:YLF lasers with excellent beam quality.