Projects per year
This thesis reports on experimental investigations of the interaction of intense (> 1018 W/cm2 ) laser pulses with solid density targets. This interaction has been known for many years to generate high energy (fast) electrons, ions, xrays and γ-rays as well as powerful shock waves and gigagauss magnetic fields. Proposed applications for such interactions include their implementation as a compact source of high energy ions to be used in the treatment of cancers and as a source of high energy electrons to induce the necessary high energy-density conditions required to achieve nuclear fusion, therefore acting as a new, clean energy source. For both applications the process of electron generation via the absorption of the laser pulse is critical and is required to be as efficient as possible, either for ion acceleration in order to reach the highest ion energies or for laser driven nuclear fusion in order to maximise energy gain of the reaction. The work in this thesis seeks to address some of these issues by investigating the processes of electron generation and the key parameters which can be controlled to optimise such processes. Across three different experiments, by modifying parameters such as laser incidence angle, plasma density profile, laser polarisation, target thickness and laser intensity, control over fast electron generation process is demonstrated. In the first of these experiments spatial control over the electron generation is demonstrated. Large laser incidence angles are used to drive fast electrons along the target surface as opposed to the along the laser axis direction using the growth of strong quasi-static electric and magnetic fields which form on the target surface. In the second experiment a controlled plasma density gradient is used to enhance the coupling efficiency of the laser into high energy electrons. This enhancement is demonstrated by both experimental results and in simulations. The simulations show that the enhancement is driven by self-focusing in the underdense region of the plasma density profile, an effect which becomes less effective at longer density scale lengths due to the onset of laser filamentation. In the final experiment an enhancement in electron generation is demonstrated due to the onset of relativistic induced transparency (RIT). Both experimentally and in simulations the onset of this process is shown to be sensitive to target thickness, laser intensity and polarisation. With the correct combination of these three parameters RIT occurs, resulting in an enhancement of over an order of magnitude in accelerated electron numbers.
|Place of Publication||Glasgow|
|Publication status||Published - 1 Jan 2013|
- laser pulses
- solid density targets
- high energy electrons
- electron generation