Injection-seeded backward terahertz-wave parametric oscillator

Abstract

Engineered quasi-phase-matching in a periodically poled nonlinear crystal has enabled backward optical parametric oscillators, where a pump photon is down-converted to counterpropagating signal and idler photons without an optical cavity. Here, we demonstrate an injection-seeded backward terahertz-wave parametric oscillator (BW-TPO) based on a slant-strip-type periodically poled lithium niobate crystal. A continuous-wave single-frequency laser is used in the BW-TPO pumped by sub-nanosecond 1064.4-nm pulses to provide an injection seed beam for the forward-propagating idler wavelength at 1065.7 nm, resulting in over a 1000-fold enhancement in backward-propagating 0.335-THz output energy, a 63% reduction of the oscillation threshold, and a quantum conversion efficiency as high as 47%. Thanks to the unique advantage of cavity-less oscillation, these improvements and stable operation in the BW-TPO are achieved without any stabilization control of either seed or oscillation modes. Our results show that such an injection-seeded BW-TPO is promising as a compact, efficient, and robust THz-wave source for a wide variety of applications.