Wavelength Dependence of Output Energy in Terahertz Wave Difference Frequency Generation Pumped by a Tunable Dual-KTiOPO$_{4}$ Optical Parametric Oscillator Source

The intensity of the output terahertz (THz) wave limits the applications of the difference frequency generation (DFG) sources. An optimum dual-wavelength pair can effectively enhance the DFG efficiency. This article indicates that the optimum dual-wavelength pair not only depend on the phase matching condition as commonly believed, but also depend on the energy product of dual-wavelength output from tunable dual-KTiOPO $_{4}$ optical parametric oscillator (OPO). By applying the measured optimum dual-wavelength pairs, an enhancement of the DFG efficiency is achieved at most frequencies (75% of the frequencies within 10–34 THz), and the highest enhancement rate of 5.1 is observed at 23.6 THz.