Low-pump-threshold mid-infrared optical parametric oscillation in periodically-poled LiNbO3

We report the generation of tunable high-repetition-rate optical pulses in the mid-infrared using synchronously pumped parametric oscillation in periodically poled LiNbO3 (PPLN). Using a Ken-lens-mode-locked Ti:sapphire laser as the pump source and a PPLN crystal incorporating grating periods of 21.0-22.4 mum, we have achieved wavelength conversion in the 4-6-mum spectral range in the mid-infrared. The use of a semi-monolithic cavity design and hemispherical focusing has permitted pulse generation in the strong idler absorption region of PPLN, resulting in a simple, compact, all-solid-state configuration with a pump power threshold as low as 17 mW and mid-infrared idler powers of up to 64 mW at 9% extraction efficiency. Signal output powers of up to 280 mW at 35% extraction efficiency are available over the 1.004-1.140-mum spectral range at 80.5 MHz and pulse repetition rates at harmonics of the fundamental Frequency up to 322 MHz have also been obtained.