Broadband Anisotropic Optical Properties of the Terahertz Generator HMQ-TMS Organic Crystal

HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along thex1andx3axes of a HMQ-TMS single-crystal, we extract both the refraction indexnand the extinction coefficientkbetween 50 and 35,000 cm(-1). We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the twox1andx3axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region.