A NEW INSTRUMENT TO MEASURE FAR INFRARED REFLECTANCE AND TRANSMITTANCE

Abstract

A new instrument to measure far infrared transmittance is described. The operation of a Martin-Puplett spectrometer which provides the light for the instrument is reviewed. The data acquisition is also discussed as is the method used to extract transmittance spectra from the raw data. A detailed description is given of the cryostat which holds the detector and the sample. The detector is a silicon bolometer with an operating temperature of 0.3 K, and the sample can be cooled to temperatures between 1.2 K and 100 K. Provision has also been made to allow application of a magnetic field as high as 18T using the high field superconducting magnet at the University of Toronto. In the future, an insert will be built to allow the instrument to measure reflectance. In order to test the apparatus, transmittance measurements with no applied magnetic field were made on a CuGeO3 single crystal. The same crystal was measured using a previously well tested Fourier transform interferometer and a 1.2K bolometer. Comparisons of the two measurements were made, and reasonable agreement was obtained. Two different filters were used to demonstrate their effect on the range of frequencies over which the transmittance can be measured. Measurements down to 5 cm^1 was easily achieved.