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Title: Laser induced gas breakdown
Author: Avery, P. K.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1979
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An experimental investigation of laser-induced gas breakdown has been carried out using 10ps and 47ns pulses of 1.0611m radiation from a neodymium:glass laser system. The focal region of the lens used to concentrate the laser radiation was observed with a photomultiplier in an effort to detect light which may not be visible to the naked eye. The majority of visual observations of the focal region reported in the literature show a strong pressure dependence of the threshold laser intensity for breakdown even under conditions for which multiphoton ionization is expected to be the dominant ionization mechanism, while reports of breakdown in which a photomultiplier was used to detect the plasma radiation in the multiphoton-dominated regime have described the expected intensity threshold plateau. Experiments were performed to examine whether the threshold intensity for air determined by the photomultiplier was strongly pressure dependent in the avalanche ionization regime in agreement with the visually determined threshold. The photomultiplier was then used to observe the pressure dependence of the threshold intensity in the multiphoton ionization regime and the expected plateau region was found for nitrogen, argon and xenon, under similar conditions to those in which visual observations had previously led to the strongly pressure dependent threshold. This is the first report of a plateau in the breakdown threshold intensity for argon or xenon irradiated by 1.06ppm radiation. Studying the increase in plasma radiation power with increasing laser-beam intensity it was found that the strongly pressure dependent threshold, is associated with much higher plasma radiation energy than the plateau region. The suggestion is made that visual observations detect the threshold for high beam absorption rather than a high degree of ionization.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available