Far-infrared properties of DAST

Using terahertz time-domain spectroscopy, we have measured the index of ref raction and the absorption coefficient of the organic ionic salt 4-N, N-dim ethylamino-4'-N'-methyl-stilbazolium tosylate (DAST). This promising organi c electro-optic material exhibits strong absorption and dispersion for freq uencies 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-ph onon origin of the resonances. A simple vibration of the anion and cation o f the salt is suggested as the origin of the exceptionally strong far-infra red absorption and the high-frequency electro-optic properties of DAST. (C) 2000 Optical Society of America. OCIS codes: 160.4330, 320.7110, 300.6270.