Plasma Lenses for Relativistic Laser Beams in Laser Wakefield Accelerators

Focusing petawatt-level laser beams to a variety of spot sizes for different applications is expensive in cost, labor and space. In this paper, we propose a plasma lens to flexibly resize the laser beam by utilizing the laser self-focusing effect. Using a fixed conventional focusing system to focus the laser a short distance in front of the plasma, we can adjust the effective laser beam waist within a certain range, as if a variety of focusing systems were used with the plasma lens acting as an adjustable eyepiece in a telescope. Such a setup is a powerful tool for laser wakefield accelerator experiments in state-of-art petawatt laser projects and allows for scanning focal spot parameters.Comment: 12 pages, 11 figure

High-resolution μCT of a mouse embryo using a compact laser-driven X-ray betatron source

High-resolution microcomputed tomography with benchtop X-ray sources requires long scan times because of the heat load limitation on the anode. We present an alternative, high-brightness plasma-based X-ray source that does not suffer from this restriction. A demonstration of tomography of a centimeter-scale complex organism achieves equivalent quality to a commercial scanner. We will soon be able to record such scans in minutes, rather than the hours required by conventional X-ray tubes

The role of levosimendan in acute heart failure complicating acute coronary syndrome: A review and expert consensus opinion

Peer reviewe

Characterisation of self-guided laser wakefield accelerators to multi-GeV energies

This thesis details experimental and theoretical work in the field of self-guided laser wakefield accelerators, characterising various aspects of the machine related to the driver laser and electron beam generation. The spectral changes to the laser pulse driving a laser wakefield accelerator were characterised. It was found that the spectral blueshift is directly correlated to the length of the plasma cavity. Spectral phase changes of the driver pulse were measured to dramatically alter the interaction. Positive second order spectral phase was measured to increase electron beam energy, its charge and the spectral blueshifting undergone by the driver pulse. The suppression of self-injection in laser wakefield accelerators operating in the highly non-linear bubble regime was observed. The use of ionisation impurity to pre-inject electrons into the plasma cavity was measured to alter the fundamental properties of the electron beam. Through particle-in-cell simulations it was shown that this effect arises from the repulsive electrostatic force from the beam load, preventing sufficient transverse momentum gain of sheath electrons. Record electron beam energies of nearly 3 GeV were measured in the self-injecting, self-guiding regime of laser wakefield accelerators. These results were obtained at higher than expected plasma densities and are thought to be a direct result of increased energy coupling due to the use of a much longer main focussing optic. Very stable injection in the self-injection regime was observed allowing for experimental measurements of peak accelerating field within the bubble. The field E = (590 ± 180) GV/m is the highest value of the electric field reported. The efficacy and long-term stability of self-guided, self-injecting laser wakefield electron acceleration was evaluated. Highest sustained laser energy to electron beam energy conversion efficiency of nearly 3% was measured. It was also shown the self-injection yields higher overall efficiencies than ionisation induced injection. Stability of injection and acceleration over more than half a thousand consecutive shots was studied and found to be directly dependent on the stability of the driving laser.Open Acces

High-quality polarised electron bunches from colliding pulse injection

Highly polarised, high current electron bunches from compact laser-plasma accelerators are sought after for numerous application. However, current proposals to produce these beams suffer from intrinsic limitations to the reproducibility, charge, beam shape and final polarisation degree. We propose colliding pulse injection as a technique for the generation of highly polarised electron bunches from pre-polarised plasma targets. Using particle-in-cell simulations, we show that colliding pulse injection enables accurate control of the spin-polarisation during the trapping of electrons, enabling high-current electron bunches with high degrees of polarisation to be generated. Bayesian optimisation is employed to optimise the multi-dimensional parameter space of colliding pulse injection, demonstrating the generation of highly polarised, high-quality electron bunches employing 100-TW class laser technology