Abstract

Doubly resonant optical parametric oscillators (DR OPOs) have simultaneous resonance of both signal and idler waves. This simultaneous resonance allows lower pump threshold and better frequency selection compared to singly resonant optical parametric oscillators. The stable operation of DR OPOs requires pump lasers with narrow bandwidth, good frequency stability, and good spatial mode quality. We used a semiconductor-diode-laser-pumped nonplanar-ring-oscillator miniature solid-state laser with its output converted to second harmonic at 532 nm for OPO pumping. The combined requirements of double resonance and conservation of energy can result in discontinuous wavelength tuning of DR OPOs. When the crystal temperature is changed, the output jumps from one spectral region to another. Stepwise tuning with continuous spectral coverage is possible when the OPO resonances are finely controlled with electrooptical or pump frequency tuning. An analysis of this tuning that considers temperature- dependent dispersion, thermal expansion, and the electrooptical and piezoelectric effects is presented. Results are compared with the observed performance of a monolithic doubly resonant MgO:LiNbO₃ optical parametric oscillator. Pulsed parametric oscillation with single-mode signal and idler waves was observed tunable from 1.01 to 1.12 μm by temperature change and an applied electric field.

© 1988 Optical Society of America