Self-seeded diode laser increases efficiency of frequency-doubling in lithium iodate
A self-seeded, gain-switched pulsed aluminum gallium indium phosphide Fabry-Perot diode laser has been used by University of Tokyo (Japan) researchers to increase frequency-conversion efficiency for production of 345-nm light in bulk lithium iodate (LiIO3). Current diode-laser-based second-harmonic generation (SHG) of ultraviolet (UV) light is based on crystals with relatively small nonlinear coefficients compared to those used at longer wavelengths.
Improving frequency conversion with self-seeding--instead of using diode laser amplifiers to increase fundamental power or resonant-cavity and quasi-phase-matched arrangements--narrows the SHG spectral bandwidth to 0.11 nm FWHM, less than a tenth of that without seeding. The resulting normalized conversion efficiency is 0.218%/W cm, which the investigators claim is four times larger than for pulses without seeding. A UV output of 0.12-µW average power was generated in a commercial 5-mm-long LiIO3 crystal using 10.5-mW, average-power 690-nm light in 500-MH¥pulse trains with 68-ps temporal width and 0.11-nm spectral bandwidth.