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Title: Laser-plasma coupling effects on spectral line shapes.
Author: Howe, Jonathan
ISNI:       0000 0001 3582 6660
Awarding Body: University of York
Current Institution: University of York
Date of Award: 2007
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This thesis presents an experimental and computational study of strong electric field effects on plasma spectral line shapes. The role of laser-driven electron plasma waves is studied for helium-like systems where atomic energy levels are weakly susceptible to external electric fields. In this case strong electric fields associated with laser driven electron plasma waves are resonant with the radiators producing modulations on line emission. In an experiment the ASTRA laser system was used to generate expanding plasma ionised to H-like and He-like states using short (picosecond) laser pulses. Spectral emission dispersed by a high dispersion toroidal spectrometer capable of high spatial and spectral resolutions is presented. Cross sections of the emission close to the target surface contains modulations on the He (3 and He I resonance lines. The modulations are interpreted using the Intra-Stark framework. The modulations in each data set were found to be emitted from and below quarter critical density. By introducing a femtosecond pulse after the picosecond pulse the modulations were reduced and, in some cases, suppressed altogether. Plasma hydrodynamics and laser-plasma coupling processes are simulated using a hydrodynamics code (EHYBRID) and post-processed to include parametric processes. Simulations suggest that high amplitude electron plasma waves are generated in the plasma underdense to the laser. Atomic kinetics and spectral lines are modelled using the CRETIN code to examine the temporal evolution of the resonance line emission. Simulated spectra are post-processed to include the effects of strong high frequency electric fields associated with the laser driven electron plasma waves. The simulated spectra reproduce the modulations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available