High-contrast, ultra-intense laser-solid interaction physics with engineered targets

The key objectives of this thesis are to understand how to efficiently couple a high power laser to a target and produce bright X-ray and energetic ion sources. The approaches taken are to use plasma mirrors to improve the laser contrast, structure the target surface to increase the laser absorption and the use of ultra thin targets for ion acceleration. The experimental work is combined with computational calculations to further develop an understanding of the laser-target physics.

The suppression of the early interaction is investigated using a double plasma mirror setup. This is studied by developing a model using geometric optics and ionisation thresholds of plasma mirrors. By using these calculations in Helios simulations it is inferred that the laser interaction with the target is delayed closer to the peak of the pulse. As a result, the target expansion is reduced to sub-micron lengths by the time the main laser peak interacts with the target.

On an experiment using silicon targets with micro-structured surfaces we observe an enhancement in the X-ray emission. A conical crystal spectrometer is used for recording the emission centralised on K-alpha. The enhancement is interpreted from comparing the emission between micro-structured and flat surfaced targets. By combining the micro-structured targets with a double plasma mirror setup, a method for engineering plasma density scale length is achieved.

By laser irradiating graphene we observe the generation of protons and carbon ions using radiochromic film and CR-39. The measurements are linked to EPOCH particle-in-cell simulations. From simulations it is inferred that the onset of relativistically induced transparency is important for producing energetic ions. The ion motion is determined by the emerging electric fields in experiment and simulations.