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Title: Studies of stimulated emission of radiation
Author: Atkinson, J. B.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1967
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Laser action has been observed on a nunber of 3p - 3s transitions in the infra-red in neutral atomic Carbon and Nitrogen. Mixtures of Helium or Neon with Carbon Monoxide or Nitrogen were excited with current pulses of up to 90amps and a duration of 2μsec. Depending on the pressure, current, and transition laser action occurred either during the current pulse risetime or in the afterglow. The laser tube was 2 metres long with a bore of 7mm, and was fitted with internal electrodes and Brewster angle end windows. The time dependence of the laser output as a function of current and pressure has been investigated and the interpretation is baaed on observations of the spontaneous emission from the upper and lower levels of the laser transitions. In addition to the laser transitions, other related transitions in Carbon and Nitrogen and transitions to the metastable and resonance trapped levels of Helium and Neon were studied. Techniques have been developed to measure the populations of these metastable and resonance trapped levels by comparing the light emitted from the side of the laser tube to the light emitted from the end of the tube along the tube axis. Absolute values for the populations of the upper and lower level of the laser transition have also been obtained without the use of a calibrated detector. The different mechanisms whereby excited states may be populated in a gas discharge are discussed, and cross-sections for the different collision processes estimated. These are used together with the measured values of populations, to determine the likely dominant processes in the afterglow. Measurements of the rates of decay of the populations of the levels in Helium, Neon, Carbon and Nitrogen show a correlation between the populations of the metastable states of Helium and Neon and the 3p levels of Carbon and Nitrogen. It is therefore proposed that the dominant excitation mechanism for the 3p Carbon and Nitrogen level is (see Table). Energy considerations require that, in general the molecule be in an excited vibrational state produced by excitation during the current pulse. From the measured populations, a cross-section for this reaction is estimated and found to be 7 x 10-16cm2, with vibrational temperatures in the region of 25,000°K.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available