Supercritical-fluid cell with device of variable optical path length giving fringe-free terahertz spectra

Abstract

An optical cell suitable for supercritical fluids was constructed for measurements of far infrared absorption spectra with terahertz radiation as a light source. It was designed to withstand temperature up to 400 K and pressure up to 15 MPa. The cell has two characteristic devices; one is diamond windows set in the Brewster angle to the incident far infrared light and the other is a variable optical path length from 30 μm to 20 mm under high pressure conditions. Using the cell, fringe-free spectra of CHF3 ranging from low-density gaseous states to high-density supercritical ones were measured in a low-energy region of 10–100 cm−1.