Ultrabroadband terahertz spectroscopy of chalcogenide glasses

Chalcogenide glasses are receiving a lot of attention due to their unique optical properties. In this paper we study the optical properties of As 2 S 3 and GaLaS glasses in a broad terahertz (THz) frequency range (0.2-18THz). Complex dispersion behavior with drastic changes of refractive index and absorption coefficient is found for both glasses. We observe the breakdown of the universal power-law dependence of the absorption coefficient due to atomic vibrations observed at low THz frequencies in disordered materials, and see the transition to localized vibrational dynamics for the As 2 S 3 compound at higher frequencies. In addition, As 2 S 3 displays two transparency regions, at 7-8THz and 12.2THz, of potential interest for future nonlinear applications in the THz range.