Intracavity terahertz generation from gallium arsenide in a fiber laser pumped type 0 doubly resonant optical parametric oscillator

Abstract

Resonant cavity enhancement results in substantial improvement in the efficiency of photonic THz-wave generation via frequency down conversion. Efficient THz wave generation was demonstrated at 2.8 THz previously by difference frequency mixing between resonating signal and idler waves of the linear-cavity type-II-phase-matched PPLN optical parametric oscillator (OPO). A new, simplified approach to resonantly-enhanced THz-wave generation in periodic GaAs, featuring (i) ring, instead of linear, OPO cavity with much higher finesse, (ii) type-0, instead of type-II-phase-matched PPLN crystal as a gain medium, resulting in much lower OPO threshold, (iii) a compact picosecond 1064-nm fiber laser as a pump source, and (iv) the use of a thin intracavity etalon with a free spectral range equal to the desired THz output frequency is presented here. Intra-cavity THz generation was performed by 2.1 μm anti-reflection coated stacks of optically contacted GaAs wafers (OC-GaAs) and diffusion bonded GaAs wafers (DB-GaAs) with periodic-inversion placed in the second OPO focal plane. Using 6.6 W of average pump power, narrowband output in the range 1.4 - 3 THz was produced with more than 130 microwatts of average power at 1.5 THz. By optimizing the OPO PPLN crystal length and spectral characteristics of the fiber pump laser and OPO the demonstrated approach can be extended to generate 1-10 mW of THz output in a compact setup.