The thermo-opto-mechanical strength of Yb:YAG gain media has enabled average power scaling of solid state lasers to the kilowatt regime in continuous-wave (cw) and short-pulse regimes. Moreover, at cryogenic temperatures Yb:YAG becomes a high-gain four-level laser, exhibiting a much lower thermal lens . However, this comes at the expense of reduced gain bandwidth limiting pulsewidths to the few-picosecond regime. As an alternative Yb:YLF gain media possess broader emission bands centered around 995 nm and 1020 nm, that potentially enable generation/amplification of sub-ps long pulses even at cryogenic temperatures . In cw operation, output powers above 220 W and a slope efficiency approaching 70% has been realized from a cryogenically cooled Yb:YLF system . A similar efficiency has also been realized from a Q-switched cryogenic Yb:YLF laser delivering 60-ns pulses around 995 nm at 10 kHz repetition rate and an average power of 50 W (efficiencies up to 82% has been demonstrated in cw regime) . Via regenerative amplification, sub-picosecond 1 mJ pulses at 10 kHz , 30 mJ pulses at 20 Hz , and 107 mJ pulses at 10 Hz has been extracted from cryogenic Yb:YLF systems operating around 1020 nm.
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