New techniques for dispersive Fourier transform spectrometry of liquids

Abstract

Dispersive Fourier transform spectrometry (DFTS) techniques are described for measuring the optical constants of liquids. Free standing wire grid polarizing and melinex beam splitters are used to cover a wide frequency range and link low and high frequency FTS data with microwave and mid infrared data respectively. Both power absorption coefficient α and refractive index n are computed as continuous functions of frequency from the same dispersive measurements and good agreement has been achieved with the power absorption coefficient spectra obtained using conventional FTS. The use of windowed liquid cells enables amplitude reflection measurements to be carried out and this not only solves the liquid vapour problem, but also permits a very thin layer (10 μm) of absorbing liquid to be used. Data are presented and discussed for water, aliphatic alcohols, halobenzenes and halogen-substituted methanes.