Microwave Interferometric Measurements of Electron Density in Laser-Generated Plasma Channels

Measurements of the temporal decay of the absolute electron density in a laser-produced plasma channel have been made with a 9.2~Ghz microwave interferometer. The plasma channels were generated by sub-picosecond laser pulses ($\lambda=$248~nm, 40~mJ per pulse) produced by a hybrid Ti:sapphire/KrF excimer amplifier system. The ultrashort pulse duration resulted in a δ-function excitation source, allowing the subsequent plasma decay to be explored without further excitation of the gas and without deconvolving the excitation source profile from the electron density decay data. The temporal resolution of the interferometer has been demonstrated to be a few nanoseconds (bandwidth of $\approx$1~GHz), and electron density decay profiles have been measured in argon and nitrogen at pressures in the range of 1-650~Torr. Gas kinetic models in argon and nitrogen have been developed, and have shown good agreement with the measured electron density profiles. Model predictions of the dissociative recombination rate constants, α_D, in argon and nitrogen are reported, \mbox{α_D (Ar)=1-6 \times 10^-6~cm³~s^-1} and \mbox{α_D (N₂)=1-3.25 \times 10^-6~cm³~s^-1}. At pressures $>$200~Torr, the reported values show good agreement with previous measurements, and in the pressure range 20-200~Torr, the values presented here are the first to be reported. The multiphoton ionization (MPI) cross section for argon, σ₍₄₎, is estimated to be in the range 10^-117-10^-118~cm⁸~s³, which is within an order of magnitude of the one previous measurement, and the experimental technique is shown to have the potential to improve the precision of this estimate.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Keister, Kathryn E.

Contributors dc:contributor

• Eden, James G.
• Cooper, S. Lance
• Hertzog, David W.
• Carney, Paul S.

• plasma
• microwave
• argon
• nitrogen
• dissociative recombination
• multiphoton ionization
• electron density
• plasma filaments

Statement dc:rights

• Copyright 2011 Kathryn E. Keister

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/24061

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/24061