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Title: Measurements of optical radiation from high-intensity laser-plasma interactions
Author: Bellei, Claudio
ISNI:       0000 0004 2687 2114
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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This thesis presents experimental and theoretical results on the interaction of high-intensity lasers with solid and gaseous targets. All the measurements that are described belong to the optical region of the spectrum. The interaction with solid targets has been investigated for two different intensity regimes. Intensities of up to 10[21] Wcm-2 have been accessed on the VULCAN laser system at the Rutherford Appleton Laboratory whereas the JETI laser system at the Institut für Optik und Quantenelektronik in Jena allowed to reach intensities of up to 4x10[19] Wcm-2 . For both regimes, the transport of relativistic electrons generated in the interactions has been investigated through measurements of the optical radiation emitted from the rear surface of the solid targets. Polarimetry and angular distribution measurements indicate that the radiation presents a high degree of polarisation and is non-isotropically emitted. It is, therefore, mainly attributed to transition radiation. A theoretical model has been developed in order to interpret and validate the experimental observations. As a result, for the high intensity regime variation of the signal strength of the transition radiation with respect to the direction of observation is attributed to the presence of mm-scale filaments. The interaction with gaseous targets has been investigated at the Astra Gemini facility at the Rutherford Appleton Laboratory, for peak intensities of up to 3x10[19] Wcm-2 in a spot size of 20 [Mu]m FWHM. In this experiment the properties of the laser pulse were studied after interaction with the targets. For this purpose, a second harmonic generation FROG device was used. This allowed to determine both the pulse duration and the temporal phase of the pulse, giving an insight on the dependence of the pulse properties with respect to interaction length and electron number density. The experimental results show that the nonlinear evolution of the pulse can lead to compression from 45 fs before the interaction to a single pulse of below 20 fs duration, after propagating in the gaseous medium.
Supervisor: Krushelnick, Karl ; Najmudin, Zulfikar Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral