Crystal length in optical parametric oscillators - Size matters!

Continuous-wave optical parametric oscillators (OPOs) with periodically-poled lithium niobate as the nonlinear medium combine a wide tuning range with single-frequency operation. Singly-resonant systems pumped by lasers with a wavelength of 1 mum have been demonstrated for more than ten years. They have pump thresholds of about 1 W, and most of them have crystal lengths of 50 mm. We show that the maximum single-frequency idler power can be increased by a factor of three by reducing the crystal length to 25 mm.