Optical rectification in a chalcopyrite AgGaSe2 crystal for broadband terahertz radiation generation

We report on optical rectification in a ⟨110⟩AgGaSe2 crystal that produces terahertz (THz) electric field pulses across the broad frequency range of 0.02–4 THz. Due to the large coherence length of the AgGaSe2 crystal (>4 times larger than that of CdSiP2 and ZnGeP2), in-phase THz radiation is produced over the entire crystal thickness of 485 μm. Furthermore, THz time-domain spectroscopy is used to determine the ordinary and extraordinary refractive indices and extinction coefficients of the uniaxial AgGaSe2 crystal across the broad spectral range of 0.5–2.9 THz, encompassing several phonon resonances.