Using terahertz time-domain spectroscopy, we have measured the index of refraction and the absorption coefficient of the organic ionic salt 4-<i>N</i>, <i>N</i>-dimethylamino-4′-<i>N</i>′-methyl-stilbazolium tosylate (DAST). This promising organic electro-optic material exhibits strong absorption and dispersion for frequencies above 1 THz at both room temperature and 83 K. No reduction in the absorption strength is observed when DAST is cooled, suggesting a single-phonon origin of the resonances. A simple vibration of the anion and cation of the salt is suggested as the origin of the exceptionally strong far-infrared absorption and the high-frequency electro-optic properties of DAST.
© 2000 Optical Society of America
Markus Walther, Kasper Jensby, Søren Rud Keiding, Hidenori Takahashi, and Hiromasa Ito, "Far-infrared properties of DAST," Opt. Lett. 25, 911-913 (2000)