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). https://www.hindigyanvishv.com/best-buy-Big-Sur-After-Rain-Hand-Soap-amazing-deal/