Development of new techniques for submillimetre wave spectroscopy of solids

Abstract

A selection of free-standing fine-wire grids with different wire spacings have been wound for use as spectroscopic components at millimetre and submillimetre wavelengths. The performance of the grids has been investigated extensively and found to be in good overall agreement, both qualitatively and quantitatively, with calculations made using a least-squares method developed by Beunen. Where discrepancies occur they are attributed to the effect of uneven spacing of the wires. A microcomputing system based on the Z80 8-bit microprocessor has been built to provide data acquisition and Fourier transformation for a Fourier spectrometer. Measurements have been made of the far infrared optical constants of KC1 and KBr crystals by dispersive Fourier transform spectroscopy at temperatures in the range 7-500K using instruments equipped with both mylar and wire grid beam dividers. The results have been used to calculate the dielectric functions and the an harmonic self energy functions of the q = 0 transverse optic modes in these crystals. The frequencies of the transversive optic (TO) and longitudinal optic (LO) modes determined from the dielectric functions are in good agreement with the accepted values, and in the case of KBr, the frequency-dependence of the an harmonic self-energy functions determined at room temperature is in good agreement with calculations made by Bruce.