Our understanding of the structure of molecules and the nature of the chemical bond has developed in tandem with our ability to measure the characteristics of the outer (valence) electrons that control chemical bonding. A key tool in this development has been photoelectron spectroscopy, whereby a high-energy burst of light removes an electron from the molecule. By measuring the energy of the outgoing electron and the direction in which it travels, we can obtain detailed information on the arrangement of the electrons and the nuclei in the molecule. Chemistry is very dynamic, with atoms and molecules in constant motion and chemical reactions defined by associated changes in structure and bonding. Measuring chemical dynamics in real time, from reactants to products, is challenging and requires probes capable of resolving the changes in the arrangement of the valence electrons responsible for chemical bonding. Using ultrashort pulses of light, we can make photoelectron spectroscopy measurements with sufficient time-resolution to track the dynamic changes in the molecular electronic structure during reactions. We will use new light sources and advanced theory to provide detailed measurements and analysis of light-induced chemical dynamics. The experiments will take advantage of high harmonic generation based light sources and high intensity lasers to monitor all of the structures important during photochemical reactions. The theory developments will combine state-of-the-art simulations of quantum molecular dynamics with new methods to calculate photoelectron spectra with high accuracy, allowing accurate images to be extracted from the experimental data to achieve a detailed mapping of the chemical reactions. This research will enable better understanding of the driving forces that control the outcomes of photochemical reactions and allow new methods to control, design, and direct chemical reactivity.

. 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. .

Advances in laser technology have enabled the focussing of light to extreme intensities, capable of creating exotic states of matter, typically characterised as high temperature plasma - the forth state of matter, in which the electrons and ion matter constituents are moving around with high velocity. New ultrahigh intensity lasers, due to come online in the next few years at international research facilities, will focus light to ten times higher intensity that is achievable at present. This will be sufficient to create an entirely new state of plasma in which quantum electrodynamics (QED) processes play an important role. This new state is the so-called QED-plasma. This state of matter is largely unexplored in the laboratory and yet will play a crucial role in many of the experiments to be performed using next generation high power lasers. While QED theory is well established for the interaction of single particles, but QED-plasmas are complex systems of very many particles. This creates a challenge as in quantum theory all possible interactions must be considered and in QED-plasmas the large number of particles gives far too many possibilities for standard QED theory to be used. While semi-classical models have been developed which include what are expected to be the most important quantum effects, these have yet to be tested experimentally. We will conduct a programme of work to test our models of QED interactions in strong electromagnetic fields for the first time using existing particle accelerators and high power lasers. We will then use this model to design experiments to generate and explore the first QED-plasma in the laboratory, which we will subsequently perform on new next generation high-intensity laser facilities. QED-plasmas are postulated to play a key role in extreme astrophysical environments such as in the extremely strong magnetic fields around pulsars, for example populating the magnetosphere with an electron-positron plasma in a cascade of antimatter production. The demonstration and investigation of the QED-plasma state in experiments will give us the opportunity to probe this physics in the laboratory for the first time.

. 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.