Terahertz generation in high purity semiconductors via 3 wave DFG and cross-reststrahlenband PM

Difference frequency generation is being used in undoped, high-resistivity GaP to generate a tunable far-infrared, or terahertz, idler wave using near-infrared pump and signal sources. We have proposed a novel phasematching technique for terahertz generation valid for DFG interactions using cross-reststrahlen band PM. The pump and signal source frequencies must be on the adjacent side of the crystal's reststrahlen band from the idler wave frequency. The formula predicts a large, but variable, tuning range around the perfectly phasematched terahertz frequency.