Intra-pulse difference frequency generation in ZnGeP₂ for high-frequency terahertz radiation generation

The highly-nonlinear chalcopyrite crystal family has experienced remarkable success as source crystals in the mid-infrared spectral range, such that these crystals are primary candidates for producing high terahertz frequency (i.e., [Formula: see text] 10 THz) electric fields. A phase-resolved terahertz electric field pulse is produced via intra-pulse difference frequency generation in a chalcopyrite (110) ZnGeP₂ crystal, with phase-matching being satisfied by the excitation electric field pulse having polarizations along both the ordinary and extraordinary crystal axes. While maximum spectral power is observed at the frequency of 24.5 THz (in agreement with intra-pulse phase-matching calculations), generation nonetheless occurs across the wide spectral range of 23-30 THz. To our knowledge, this is the first time a chalcopyrite ZnGeP₂ crystal has been used for the generation of phase-resolved high-frequency terahertz electric fields.