Efficient ultraviolet-light (345-nm) generation in a bulk LiIO_3 crystal by frequency doubling of a self-seeded gain-switched AlGaInP Fabry–Perot semiconductor laser

A self-seeded gain-switched semiconductor laser is applied as a fundamental optical source to second-harmonic generation, and improvement of frequency-conversion efficiency is demonstrated. 345-nm ultraviolet light of 0.12-$\mathit{\mu }\mathrm{W}$ average power is generated in a bulk ${\mathrm{LiIO}}_3$ crystal for 690-nm fundamental light of 10.5-mW average power, which is composed of 500-MHz pulse trains emitted from an AlGaInP diode laser with a 68-ps temporal width and a 0.11-nm spectral bandwidth. It is clearly shown that the narrowing of the spectral bandwidth by the self-seeding technique gives rise to a normalized conversion efficiency of $0.218\%/\mathrm{W} \mathrm{cm}$, which is four times larger than that for pulses without seeding.