Resonant frequency quadrupling of a mode-locked diode-pumped Nd:YLF laser

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Abstract
We report on a novel method of efficient frequency quadrupling of a mode-locked diode-pumped Nd:YLF laser to 262 nm in the ultraviolet region of the spectrum using two external ring enhancement cavities in series. With 6 W of pump power the mode-locked Nd:YLF laser produced 1 W of power incident into the first enhancement cavity. The fundamental has been resonantly frequency doubled using a crystal of lithium triborate with a conversion efficiency of 60% to produce 600 mW of usable mode-locked output at 523.5 nm. Fourth-harmonic radiation was generated by frequency doubling this green output in a second ring enhancement cavity using a crystal of beta-barium borate. Conversion efficiencies from green to ultraviolet of 11% have been achieved, producing a maximum usable average power at 262 nm of 42 mW in picosecond pulses.