Near-degenerate doubly resonant synchronously pumped OPO for intracavity THz generation

Abstract

We developed a source of terahertz-frequency radiation using intracavity difference-frequency mixing in three types of micro-structured GaAs between the signal and idler waves of a doubly resonant synchronously pumped optical parametric oscillator (DRO). The pump, signal, and idler waves were type-II quasi-phase-matched (QPM) by a 10-mmlong magnesium-doped periodically poled LiNbO 3 crystal. The oscillator operated near frequency degeneracy with signal and idler bandwidths of 100-200 GHz. The DRO was pumped by a CW-mode-locked laser with a 1064-nm wavelength, 7-ps pulse width, 50-MHz repetition rate, and average power of 10 W. The cavity round-trip power losses were 4-5% for each wave, and at the largest pump power as much as 120 W of total signal and idler average power was stored inside the cavity. We developed an electronic locking feedback network that provided >15 minutes of stable DRO operation with over 100 W of intracavity average power and power fluctuations of 5-10%. The signal and idler pulse widths were characterized with an extracavity sum-frequency generation process between the pump and resonant OPO pulses. We developed a split-step Fourier propagator to model the temporal properties of the signal and idler pulses, and we found excellent agreement with experimental results.