Frequency-doubling periodically poled lithium niobate generates high power at 473 nm
In CLEO `97 paper #CPD32, Markus Pollnau from the Optoelectronics Research Centre (Southampton, England) reported producing an average output power of 450 mW at 473 nm from a diode-pumped Nd:YAG laser emitting at 946 nm and frequency-doubled with quasi-phase-matched periodically poled lithium niobate (PPLN). The 0.5-mm-thick, 15-mm-long PPLN sample had a grating period of 4.5 µm, and photorefractive effects in the sample were minimal.
For harmonic generation, the Nd:YAG laser was operated at average powers in the 1- to 1.5-W range. Pulsed output at the relaxation oscillation frequency, typically 160 kHz, produced 300-ns pulses. This behavior was deliberately induced by feedback from the uncoated PPLN surface together with a piezoelectrically driven dither of the output coupler. These conditions produced an average power of 1.13 W inside the PPLN that was focused to a spot radius of 30 µm and generated blue output power of 450 mW, corresponding to a 40% conversion efficiency. With laser optimization and coated PPLN, Pollnau expects the output powers to exceed 1W.