Far-infrared optical constants of CO2 near the critical point measured by terahertz spectroscopy

The optical index constants of CO2 at critical density are measured by terahertz (THz) time-domain spectroscopy (TDS–THz) in the frequency range 0.1–1.5 THz. Since supercritical CO2 is usually presented as a “universal” solvent, we systematically study the refractive index variations in the vicinity of its critical point along the critical isochore by scanning temperature from 295 to 308 K to explore the liquid, the gas, and the supercritical states. Density changes with temperature result in refractive index variations that are found to fit the Lorenz–Lorentz relationship in the THz frequency range.