The interaction of a laser pulse of relativistic intensity (≥1×1018 Wcm−2) with a solid target results in the creation of a quasi-electrostatic field at the rear surface of the target. This field is strong enough (TVm−1) to ionise and accelerate ions from the target surface via the Target Normal Sheath Acceleration (TNSA) mechanism. The resulting beam has many desirable properties for a large range of potential applications. The work presented in this thesis aims at optimising and controlling the ion beam properties. Firstly, an investigation of laser driven ion acceleration using ultrahigh contrast (1010), ultrashort (50 fs) laser pulses focused to intensities up to 1021 Wcm−2 on thin foil targets is presented. It is found that irradiation at normal (0◦) incidence produces higher energy ions than oblique incidence (35◦), contrasting sharply with previous work at lower intensities. These findings are confirmed by 1D boosted PIC simulations and can be explained by the acceleration of fast electrons being dominated by a new absorption process. The effects of target composition and thickness on the acceleration of carbon ions are also discussed and compared to calculations using analytical models of ion acceleration. Next, an investigation of the transverse refluxing of fast electrons in targets of limited lateral size is reported. The targets were irradiated by high intensity (∼1×1019 Wcm−2), picosecond laser pulses. The maximum energy of the resulting TNSA proton beams is found to increase with decreasing target surface area. This is explained by the presence of a laterally spreading electron population that reflects off the target edges and enhances the TNSA accelerating field. In addition it is demonstrated that this laterally refluxing electron population can be used to control the spatial intensity distribution of the TNSA proton beam, by changing the geometry of the target. This technique offers encouraging prospects for many applications of laser accelerated ions. Finally, a characterisation study of debris emission generated by the interaction of high power laser pulses with solid targets is presented. Targets of thickness ranging from 1 mm to 5 nm were irradiated by high intensity (∼1×1020 Wcm−2), picosecond laser pulses. The resulting debris emission is found to be directed along the target normal axis at both the rear and front of the target. The front emission profile is found to be similar to a plasma expansion profile. Hollow debris depositions of radius increasing with target thickness are measured from the target rear surface. This emission profile is explained by the propagation and breakout of a laser driven shock at the rear of the target.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:570515 |
| Date | January 2012 |
| Creators | Tresca, Olivier |
| Publisher | University of Strathclyde |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=16842 |
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