The proposed research project focuses on theoretical and numerical investigations of the physics of laser-matter interaction at ultra-high laser intensities, in the range 10^22-10^24 W/cm^2. These intensities will soon be achievable at multi-petawatt laser facilities, such as the 800MEuro extreme light infrastructure (ELI) and APOLLON-10P. These facilities will enable the exploration of new fundamental physical processes such as radiation reaction, relativistic electron dynamics, electron-positron pair production and the generation of relativistic ions. Electrons produce significant synchrotron radiation at laser intensities above 10^22 W/cm^2 giving rise to the radiation reaction force that strongly affects the photon emission spectrum and the overall plasma dynamics. Due to the intense electromagnetic fields involved, quantum effects will become important for laser intensities above 10^23W/cm^2, resulting in the production of copious amounts of electron-positron pairs. My proposal aims to explore the underpinning physics of these proposes theoretically and numerically. The results will be used to guide the design and interpretation of related experiments using these new ultraintense laser systems. The proposed research project opens up new directions in ultra-relativistic plasmas that are subject to quantum electrodynamics (QED) processes. For example, to date, the role of the plasma ions on the high energy synchrotron radiation and electron-positron pair production, is poorly understood and has never been explored experimentally. It is often suggested that the interaction of a short laser pulse with plasmas is dominated by the electron dynamics and that the ions play a secondary role due to the longer timescales over which they react. Although this may be true for lower laser intensities, the situation becomes more complicated in the case of ultra-relativistic laser pulses for which the quiver electron energy could be comparable with the ion rest mass. The collective effects driven by the ion response will be investigated in both semi-classical plasmas and quantum plasmas. A kinetic theory of laser energy absorption accounting for ion response will be developed over this proposed research project. Future experiments, which will test the predictions of the theory and simulations, will also be designed. The project involves collaboration with a number of leading researchers in high field laser-plasma interaction physics, both in the UK and in Europe. It also involves a close collaboration with an experimental team at the University of Strathclyde and with the ELI-NP high field science working group.

. The fundamental properties of optics are well understood at moderate light intensities. However, at the highest intensities capable of being produced using state-of-the-art lasers, many new and useful optical phenomena arise. When a high intensity laser pulse is focused onto a medium it generates a plasma and can drive extreme temperatures and intense electric and magnetic fields. This results in the production of beams of high energy particles and radiation with unique properties, which are opening up new frontiers in science and new applications. The plasma electrons quiver in the intense laser field at velocities close to the speed of light, which changes fundamental properties of the plasma, such as its refractive index. The fact that the particle motion and nonlinear optical properties dynamically evolve in response to inter-action with the laser pulse means that the plasma can act as an active optical element. If harnessed, this would provide researchers with a tool to dynamically control both the properties of ultraintense laser light and the beams of charged particles and radiation produced. Great progress has been made in controlling the collective response of electrons to intense laser pulses propagating in low density (transparent) plasma, resulting in the production of high energy, ultrashort bunches of electrons in a low divergence beam. The situation is more complex in the case of solid density plasma, used for example for ion acceleration and high harmonic generation. The dense plasma acts as a mirror (a plasma mirror), which reflects a significant portion of the laser beam. At ultrahigh laser intensities, however, the nonlinear motion of the plasma electrons results in relativistic optical phenomena which can render the dense plasma transparent. Our proposed research focuses on exploring relativistic plasma optics in ultrathin foils. Such targets initially act as a plasma mirror, reflecting laser light, and evolve over the course of the interaction to become relativistically transparent. This transient behaviour offers a promising route to controlling charged particle acceleration in dense plasma. During the opaque phase of the interaction, strong longitudinal electrostatic fields are generated, resulting in forward-directed electron and ion beams, which can be controlled using relativistic optical effects induced as the laser propagates through the target during transparency. We will investigate this approach as a means of dynamically controlling fundamental properties of the transmitted intense laser light and the resulting high energy particles and radiation. We will use the complementary capabilities of the new 350 TW laser at the Scottish Centre for the Applications of Plasma Accelerators, in which new techniques can be developed and optimised over time, and the Gemini and Vulcan lasers at the Central Laser Facility, which offer higher power and dual beam capability. We will also perform closely coupled simulations using high performance computers. This will allow us to investigate the potential for developing relativistic plasma optics processes for the dynamic control of the spatial, temporal and polarisation properties of ultraintense laser pulses. We will investigate the use of this approach for controlling the properties of beams of high energy particles and radiation produced in the interaction. Together with our international partners at the next-generation extreme light infrastructure laser facilities in the Czech Republic and Romania, we will also investigate the physics of relativistic optics and plasma dynamics at ultrahigh intensities, for which high field processes will modify the underpinning physics. We will develop a clear understanding of ultrahigh intensity optical processes, their potential use in developing plasma optical and photonic devices and the dynamic control of particle and radiation production in dense plasma. .

. We propose to create new capability and capacity for collaborative high power laser-plasma research to underpin the development and application of laser-driven radiation sources, using three new beamlines and experiment stations at the Scottish Centre for the Application of Plasma-based Accelerators, SCAPA. Each of the beamlines will be configured in a unique way and with a focus on a specific category of laser-plasma interactions and secondary sources, to create a complementary suite of dedicated beamlines. This approach is required to enable the development and optimisation of laser-plasma sources from the realms of scientific investigation to real-world applications. It enables long-term investment in the optimisation and stabilisation of the beams and largely eliminates downtime for rebuilding experiments, thus enabling efficient and effective use of high power laser beam time. The equipment will support an extensive research portfolio in laser-plasma physics and multidisciplinary applications, with an emphasis on radiation sources and healthcare applications. The unique properties of laser-driven radiation sources make them attractive both as tools for science (e.g. femtosecond X-ray sources for probing the structure of matter) and for applications in a variety of sectors including: healthcare (e.g. imaging and radiotherapy); industry (e.g. penetrative probing and assay) and energy (e.g. testing the integrity of stored nuclear waste). The strategic development of this field requires a balanced programme of dedicated university-scale and leading-edge national laser facilities. The proposed beamlines will complement existing and planned expansion of national facilities at the Central Laser Facility, providing new capability and capacity to enable UK research groups to remain at the forefront of this research area and help promote international collaboration. The research will be performed collaboratively with groups from across the UK and sustained mainly through collaborative research grants. The new suite of beamlines will promote exchanges between academia and industry, and enable engagement of the UK research community with large international projects, such as the Extreme Light Infrastructure, ELI. It will also provide a unique interdisciplinary training platform for researchers. .

The lab in a bubble project is a timely investigation of the interaction of charged particles with radiation inside and in the vicinity of relativistic plasma bubbles created by intense ultra-short laser pulses propagating in plasma. It builds on recent studies carried out by the ALPHA-X team of coherent X-ray radiation from the laser-plasma wakefield accelerator and high field effects where radiation reaction becomes important. The experimental programme will be carried out using high power lasers and investigate new areas of physics where single-particle and collective radiation reaction and quantum effects become important, and where non-linear coupling and instabilities between beams, laser, plasma and induced fields develop, which result in radiation and particle beams with unique properties. Laser-plasma interactions are central to all problems studied and understanding their complex and often highly non-linear interactions gives a way of controlling the bubble and beams therein. To investigate the rich range of physical processes, advanced theoretical and experimental methods will be applied and advantage will be taken of know-how and techniques developed by the teams. New analytical and numerical methods will be developed to enable planning and interpreting results from experiments. Advanced experimental methods and diagnostics will be developed to probe the bubble and characterise the beams and radiation. An important objective will be to apply the radiation and beams in selected proof-of-concept applications to the benefit of society. The project is involves a large group of Collaborators and Partners, who will contribute to both theoretical and experimental work. The diverse programme is managed through a synergistic approach where there is strong linkage between work-packages, and both theoretical and experiential methodologies are applied bilaterally: experiments are informed by theory at planning and data interpretation stages, and theory is steered by the outcome of experimental studies, which results in a virtuous circle that advances understanding of the physics inside and outside the lab in a bubble. We also expect to make major advances in high field physics and the development of a new generation of compact coherent X-ray sources.