An Ellipsometric Technique with an ATR Module and a Monochromatic Source of Radiation for Measurement of Optical Constants of Liquids in the Terahertz Range

Measuring the optical constants of liquids, especially water-containing solutions, is very difficult in the terahertz range. The well-known methods of measurement of the refractive index and absorption coefficient in this range include time-domain spectroscopy and Fourier-transform spectrometry. We have developed a highly sensitive ellipsometry method for measuring the optical constants of liquids using the tunable monochromatic radiation from the Novosibirsk free-electron laser. The ellipsometer is supplemented with an internal reflection module for the measurement of highly absorbing samples. The angle of incidence on the sample in the silicon prism of the module has been optimized for maximum sensitivity to parameters to measure. Measurements of the optical constants of various liquids have been performed, and a sensitivity of 0.01 has been demonstrated.