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Title: High harmonic generation from relativistic laser-nanofoil interactions
Author: Cousens, Steven
ISNI:       0000 0004 5915 8822
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2015
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The interaction of intense laser pulses with solid targets has shown great promise in recent years as a source of coherent, sub-femtosecond bursts of extreme-ultraviolet radiation, via various high harmonic generation mechanisms. For applications in ultrafast science, the temporal and spatial characteristics of these pulses must be carefully understood and controlled. In this thesis, nanometer-scale foil targets are investigated as a target type for these high harmonic generation processes. Here, the first reported experimental observations of high harmonic generation in reflection from nanofoils in a normal incidence geometry are presented. The intensity of the harmonics is observed to depend strongly on target thickness. In particular, the thinnest (- 5 nm) targets showed no harmonic emission, but their intensity increased with foil thickness up to a plateau at -300 nm. This dependence is investigated and explained using particle-in-cell simulations. High harmonic generation in the forward direction from laser-nanofoil interactions at normal incidence is also investigated in this thesis. Experimental observations of harmonic spectra, presented here and previously in the literature, show the appearance of even-numbered harmonics, though conventional models and 1-dimensional simulations suggest that only odd orders should be present. Their appearance is investigated and explained here using 2-dimensional particle-in-cell simulations. This thesis also presents experimental results which suggest that harmonic generation in the forward direction from nanofoils can be controlled by modifying the ellipticity of the driving laser pulse, such that the intensity of harmonics decreases when the driving pulse is made more circular. Finally, this thesis investigates the use of driving pulses with time-dependent ellipticity, in order to confine the high harmonic generation mechanism to a small temporal window, and to achieve an isolated attosecond pulse
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available