Practical urea optical parametric oscillator for tunable generation throughout the visible and near-infrared

The optical parametric oscillator (OPO) using the urea crystal is reviewed. This oscillator has demonstrated promise as a new solid-state source of tunable, coherent radiation throughout the visible and the near infrared spectral regions. New experimental results relating to the urea OPO are also discussed. A practical OPO has been constructed utilizing a crystal of relatively short length (13 mm), which can be grown comparatively easily, and this oscillator has been demonstrated to be continuously tunable from 499 nm to 1.23 μm. The possibility of extending the tuning curve still further through the use of an alternate pump source has been examined. Parametric fluorescence in urea pumped by the fourth harmonic of Nd:YAG laser output (266 nm) has been observed for the first time.