Experimental study of coherence phenomena in electric dipole systems at millimetre wavelengths

Abstract

The work described in this thesis is concerned with the
development of millimetre wave spectrometers and their application to the study of coherence phenomena in a system of electric dipoles. The investigations reported here were aimed at developing measurement techniques at millimetre wavelengths using harmonics of an 8 millimetre
klystron. The difficulties of constructing 4mm and 2mm components are considerable because of the small dimensions and tolerances involved and a consideration in the work was to keep the number of these milli­metre components to a minimum.
Firstly, an outline of the techniques for generation and
detection of millimetre waves is given. A description of the spectro­meters along with the fabrication of components is also given in some detail. The various resonant cavities which were fabricated and checked during these investigations are discussed.
Carbonyl sulphide and formaldehyde were used as working
substances to test these spectrometers. The results obtained at 4mm and 2mm wavelengths are given.
Experimental results on molecular ringing in OCS using
72.976 GHz transition are given along with calculations for relaxation times and line widths. The results were obtained by using simple crystal video detection. The simplicity of the scheme shows its potential as a technique for measurement of relaxation mechanisms and line widths.
Experimental results on molecular ringing in ammonia both in bulk gas and the beam maser (23.870 GHz) at 12.5mm wavelength are also discussed.
Investigations on the 000 - 101 transition in formaldehyde at 72.838 GHz showed that this transition was too weak for the molecular ringing to be observed. The suitability of this transition for beam maser operation was then studied in some detail and experimental work was carried out to solve a number of basic problems involved in the construction of such a device. The discussion is terminated with suggestions of how this work might be extended.