Linear and nonlinear properties of chalcogenide glasses in the terahertz frequency

Terahertz (THz) waves have the potential to improve a wide range of devices in the space, defense and semiconductor industries as well as offering the possibility of investigating various molecules of interest in biology, medicine, art etc. For this reason, THz sources, detectors and passive linear components have greatly been developed in recent years. However there is still no any non-linear device available. This is mainly due to the lack of the rigorous investigation of non-linear characteristics of materials in the THz range. We chose to investigate chalcogenide glasses due to their high nonlinear coefficients in the optical range, which might suggest pronounced nonlinear behavior also at THz frequencies. Here we present measurements, both linear and nonlinear, of As₂S₃ and As₂Se₃. For the linear measurements we employed a combination of THz time-domain spectroscopy setups. In the low frequency range we used a standard THz-TDS setup based on photoconductive switches while in the higher frequency domain we used an air biased coherent detection (ABCD) setup. This allowed for a wide frequency range (from 0.2 to 18 THz) investigation of the refractive index of the glasses. The nonlinear coefficient in the THz range was investigated using a lithium niobate based setup that allows us to reach electrical field strength exceeding 400 kV/cm. Results from both investigations will be presented during the talk.