Browsing by Author "Morris, Stuart"
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Item Open Access Characterising bremsstrahlung and non-linear Compton scatter in high intensity laser-foil interactions(Cranfield University, 2020-01-08 09:53) Morris, StuartNon-linear Compton scatter (NCS) and bremsstrahlung radiation both contribute to the X-rays produced in laser-solid interactions. While it is expected that NCS will efficiently generate X-rays for next generation lasers, the weaker NCS yields from laser-solid interactions in existing facilities have not yet been observed due to the bremsstrahlung background. This work attempts to derive a quantitative description of the bremsstrahlung efficiency, for interactions between ultrahigh-intensity short-pulse lasers and thin-foil targets. This model was tested against simulations from the particle-in-cell code EPOCH, which has been extended to include bremsstrahlung modelling capabilities. The relative efficiencies of bremsstrahlung and NCS will be compared to seek NCS signatures for experimental observation.Item Open Access Highly efficient conversion of laser energy to hard X-rays in high intensity laser-solid simulations(Cranfield University, 2022-01-13T11:21:10Z) Morris, StuartWe present simulations which predict significantly higher laser to X-ray efficiencies than those previously found in high intensity (1020-1022 Wcm-2) laser-solid simulations. The bremsstrahlung emission is shown to last for 10-100 ps, which is difficult to model with conventional particle-in-cell (PIC) codes. The importance of collective effects is also demonstrated, showing the limitations of Monte Carlo modelling in these systems. A new, open-source hybrid-PIC code with bremsstrahlung routines has been developed to model this X-ray production. Special boundary conditions are used to emulate complex electron refluxing behaviour, which has been characterised in 2D-PIC simulations. The peak X-ray efficiency was recorded in thick gold targets, with 7.4% conversion of laser energy into X-rays of energy 1 MeV or higher. The target size is shown to play a role in the conversion efficiency and angular distribution of emitted X-rays, and a simple analytic model is presented for estimating these efficiencies.Item Open Access When Multipetawatt Lasers Strike! The Physics and Applications of Laser Beams Hitting Solids(Cranfield University, 2020-12-07 16:34) Morris, StuartWhen we talk about extremely powerful lasers, it's easy to conjure up images of spies strapped to tables, Sci-Fi guns and planet destroyers, but facts are often stranger than fiction. Modern lasers on the intensity frontier are capable of focussing huge amounts of light energy into tiny, micron-scale focal spots over less than a trillionth of a second in duration - creating an incredibly high energy density. When such a pulse strikes something solid, we end up with a bright flash of X-rays, ion beams and even antimatter can be generated in the extreme fields - but how? And what applications can such exotic particles provide?