Prism-shaped Fabry-Perot etalon for absorption measurement in the terahertz range

A solid-state prism-shaped Fabry-Perot interferometer allows absorption measurements using a backward wave oscillator (BWO) continuous-wave source in the terahertz range. When a liquid sample is placed on the prism surface it affects the total internal reflection, thus it can be considered as being optically inside the cavity. The wavelength is scanned and the spectra obtained are Fourier analyzed for the absorption determination.