Widely Tunable High-Repetition-Rate Terahertz Generation Based on an Efficient Doubly Resonant Type-II PPLN OPO

We demonstrated a compact, widely tunable, and monochromatic high-repetition-rate terahertz (THz) source based on difference frequency generation in a GaSe crystal. The dual-wavelength pump laser was a doubly resonant near-degenerate type-II periodically poled LiNbO3 (PPLN) optical parametric oscillator (OPO), intracavity pumped by a 1.064-μm Q-switched Nd:YVO4 laser operating at 25 kHz. The PPLN OPO covered the wavelength range of 2072-2186 nm through temperature tuning with a 55-mm-long nonlinear crystal, and the maximum output power was 3.27 W. The generated THz wave was continuously tunable from 0.24 (1250 μm) to 3.78 THz (79 μm) with the maximum average output power of 1.8 μW at 1.57 THz. Such a compact and portable THz source has great potential for spectroscopy and imaging applications.