Spectroscopic techniques at millimetric wavelengths

Abstract

The design and construction of a complete microwave spectrometer operating at 35 Gc/s is described. The receiver is of the superheterodyne type with an intermediate frequency of 45 Mc/s; the local oscillator signal is derived by a novel method from the output of the monitor klystron. A superconducting magnet is used, capable of producing steady magnetic fields up to 42.6 kilo-oersteds. A second spectrometer is described which uses the same magnet and cryogenic system as the other spectrometer but which has a completely different microwave section. This equipment has been used to measure spin-lattice relaxation times in ruby and sapphire at 35 Gc/s using a single reflex klystron producing a pulse power at the specimen of about 10 microwatts. The results are compared with those obtained by the standard pulse saturation method and are shown to agree within experimental error. A third spectrometer operating at 70 Gc/s by harmonic generation from 35 Gc/s has been constructed and used to measure directly the relaxation times in the same specimens, using microwave pulses of less than 2 microwatts at the specimen. The results are compared with those at 35 Gc/s and a value for the frequency dependence of relaxation time in this region is calculated. Preliminary experiments with a superheterodyne receiver at 70 Gc/s ore described; the complete 70 Gc/s superheterodyne spectrometer is powered from a single 35 Gc/s reflex klystron. A special case of subharmonic mixing has been found to be more efficient with this system and suggestions for improving the performance are given. The uses of the microwave diode as a low-level detector, mixer, modulator and harmonic generator are described as they occur in the text.