Accurate Radiometric Measurements on Low-Loss Polymers at Submillimetric Wavelengths

The method of Fourier spectrometry has been employed with great effect in the measurement of the optical, and hence dielectric, properties of materials in the submillimeter-wave region. Improved experimental techniques, including the use of cooled detectors, phase modulation, and stabilized sources, have led to higher radiometric accuracy in these measurements. This paper discusses transmission measurements on low-loss polymers, obtained with a Michelson interferometer and a lamellar grating interferometer. The results demonstrate the high accuracy with which absorption coefficients can be measured for low-loss materials. The factors which limit the absolute accuracy of the measurements are discussed.