RTA-based optical parametric oscillator emits from 2.53 to 3.26 µm at room temperature

RTA-based optical parametric oscillator emits from 2.53 to 3.26 µm at room temperature

Researchers at the University of St. Andrews (Fife, Scotland) and Royal Institute of Technology (Stockholm, Sweden) demonstrated a continuous-wave (CW) singly resonant poled-RTA (RbTiOAsO4) based optical parametric oscillator (OPO) that delivers more than 200 mW of power across a tuning range from 2.53 to 3.26 µm at room temperature. The output wavelength was controlled by tuning the Ti:sapphire laser, and the system exhibited a maximum efficiency of 43%.

Until now, periodically poled lithium niobate (PPLN) has been popular for singly resonant OPOs because the pump-power requirements can be fulfilled by diode-pumped solid-state lasers. The drawbacks of PPLN, however, include thermal lensing and phase mismatch at moderate power levels and a requirement for operating above room temperature to avoid photorefractive damage to the crystal. Meanwhile, although periodically poled RTA requires higher pum¥energies--it has a lower nonlinear coefficient and is available only in shorter crystal lengths than PPLN--the intracavity pumping scheme allows room-temperature operation with little thermal lensing. In this case, the OPO used a 4.5-mm-long RTA crystal, whereas PPLN crystals used in singly resonant OPOs are typically about 50 mm long. With longer RTA crystals, the researchers expect to achieve downconversion efficiencies approaching 100% at u¥to 1-W output.