Experimental investigation of the interaction between the electron gas and the excited atoms in a plasma by means of a xenon laser
Freiberg, Robert Jerry
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https://hdl.handle.net/2142/25043
Description
Title
Experimental investigation of the interaction between the electron gas and the excited atoms in a plasma by means of a xenon laser
Author(s)
Freiberg, Robert Jerry
Issue Date
1966
Doctoral Committee Chair(s)
Goldstein, L.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
electron gas
lasers
xenon laser
gas density measurements
plasma
electron and atom interactions
Language
en
Abstract
The study of the interaction between the electron gas and the atoms in
excited states has been undertaken for a gas discharge situated in a high
gain optical cavity. Of particular interest is the effect of lasering upon
this interacti.on. Spatially resolved electron density and electron temperature
measurements are presented for a DC excited 3.51 P. (5d
33
-76P22) xenon
laser operating in a capillary bore tube over a pressure range of 12.5 to
25.5 m Torr. Anode directed gradi,ents in the electron and neutral gas ,densities
are observed and are attributed to electrophoretic effects present in
the closed capillary discharge tube. As a result of these gradients, the
local population inversion along the axis of the tube varies and, consequently.
affects the output of the 3.51 jJ. laser. The influence of lasering upon these
low-pressure capillary xenon discharge,s is investigated experimentally by
periodically spoiling the Q of the laser cavity by means of a mechanical
chopping wheel. It is observed that lasering noticeably alters both the
state of the electron gas and the populations of the excited xenon atoms.
The cU:t'rent of the DC exci.ted discharge is quenched up to 0.02 per cent during
lasering due to laser-induced variations of the electron density and mean
energy. Spatially resolved microwave cavity measurements indicate that the
electron number density may experience i,ncreases and decreases depending
upon local discharge condj.tions. Microwave radiometric measurements reveal
that the electron temperature is also affected by lasering. Variations in
the microwave cavity Q and in the electron drift velocity due to lasering
are in good qualitative agreement with the radiometric data. Confirming
spectroscopic observations of laser-induced changes in the spontaneous
radiation along the discharge tube are presented. It is demonstrated that
excitation of the 6s metastables via electronic impact is instrumental in
populating the lower laser level and contributes to a reduction in the local
population inversion. Evidence for various radiative and collisional mechanisms
responsible for the propagation of the .laser-induced perturbation
from the 5d
33
and 6P22 levels to other excited levels is also presented.
It is suggested that laser media in general can be analyzed and improved
upon by studying the laser-induced changes in the excitation and. relaxation
processes.
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