Efficient cw synchronously pumped optical parametric oscillation beyond 5 /spl mu/m in periodically poled lithium niobate

Periodically poled lithium niobate (PPLN) offers many attractive features for optical parametric oscillation (OPO). These include high nonlinearity and noncritical quasi-phase-matching in a wide spectral range, making it well-suited to synchronously pumped operation. Using a cw mode-locked 1047-nm pump, we recently demonstrated a low-threshold singly resonant oscillator tunable over the range 1.67-2.8 /spl mu/m. In this contribution we report a major extension of this tuning range, demonstrating singly resonant operation in the range 1.3-5.3 /spl mu/m, while still retaining low threshold and high efficiency. Additionally we have observed oscillations with idler wavelengths out to 6.3 /spl mu/m. This now offers a widely tunable source covering wavelengths well into the mid-IR. This is made possible by the use of PPLN, which allows operation at longer wavelengths than bulk lithium niobate. In addition, the high round trip gain in pulsed pumping of PPLN-based OPOs allows generation of coherent, tunable radiation even in spectral regions where the crystal is highly absorbing. Thus, pumping with a mode-locked 1047-nm Nd:YLF laser, we were able to generate 10 mW of idler average power at 5.3 /spl mu/m for 800 mW of incident pump power, with an oscillation threshold of under 300 mW. We also present results of the coupled-wave analysis of parametric oscillation in the presence of idler absorption.