Abstract

Terahertz (THz) technology in the frequency range of 0.1-30 THz has attracted considerable attention for numerous applications including THz time-domain spectroscopy, ultrafast dynamics by phonons and resonant modes as well as non-destructive inspection and imaging [1]. The most common laser-based approaches generating intense THz waves are based on nonlinear processes in plasma, optical rectification (OR) and difference frequency generation (DFG) in inorganic nonlinear crystals and large-scale semiconductors, but these methods show some constraints for realization of intense broadband THz sources [2]. Recently, organic crystals turned out to be very promising materials for efficient THz wave generation and detection. In particular, benchmark organic electro-optic crystals possess much larger optical nonlinearity than inorganic crystals. They can provide excellent optical-to-THz conversion efficiency at room temperature, enabling also to generate ultra-broadband THz spectra via nonlinear optical processes [3]. In addition, diffraction-limited THz waves can be easily achieved without sophisticated pumping and pulse shaping. In the present work, we report efficient ultra-broadband THz wave generation in a new acentric core nonlinear organic crystal, i.e. OHQ-T (2-(4-hydroxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate, for the first time. The as-grown OHQ-T crystal exhibits optimal molecular packing for maximizing the electro-optic and nonlinear responses. For efficient broadband THz wave generation, velocity matching between the optical pump and THz waves and their absorption properties are important factors. Therefore, it is desirable to find an optimal crystal thickness.

© 2015 IEEE