Millimetre polarisation spectrometer for paramagnetic gas molecules

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Abstract
Describes a new spectrometer for investigation of paramagnetic gases in the millimeter range (50 to 120 GHz) using the resonant Faraday effect and circular dichroism induced by a longitudinal magnetic field. The interaction between molecules and a linearly polarised resonance radiation produces a change in the polarisation of the transmitted light. A heterodyne detector is used to observe this modification on a black background by monitoring the transmitted wave through a crossed polariser. Possibilities of the spectrometer are discussed, especially its sensitivity (about 7*10-11 mm-1 at 60 GHz), and its application to the measurement of absolute line intensity are pointed out. Typical results on O2 molecules and SO free radicals both in linear and nonlinear spectroscopy are given.