THz-wave generation inside a high-finesse ring-cavity OPO pumped by a fiber laser

Abstract

Substantial improvement in the efficiency of photonic THz-wave generation via frequency downconversion results from resonant cavity enhancement. Previously, efficient THz wave generation was demonstrated at 2.8 THz by difference frequency mixing between resonating signal and idler waves of the linear-cavity type-II-phase-matched PPLN optical parametric oscillator (OPO). We present 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-IIphase- 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. 2.1 μm anti-reflection coated stacks of optically contacted GaAs wafers (OC-GaAs) and diffusion bonded GaAs wafers (DB-GaAs) with periodic-inversion were placed in the second OPO focal plane for intracavity THz generation. Narrowband output in the range 1.4 - 3 THz was produced with more than 130 microwatts of average power at 1.5 THz using 6.6 W of average pump power. The demonstrated approach can be extended to generate 1-10 mW of THz output in a compact setup by optimizing the OPO PPLN crystal length and optimizing spectral characteristics of the fiber pump laser and OPO.