Quantum phenomena in high-intensity laser-matter interactions

A new era of high-intensity laser experiments has begun.

Recent UK experiments, in which beams of ultra-relativistic electrons were collided with intense laser pulses, have shown that it is possible not only to use intense lasers to probe fundamental physics, but also to generate radiation sources with unique properties, which find applications across the sciences. Such experiments are extremely challenging, and despite recent successes there is disagreement over to what extent quantum effects have been observed. Discrepancies between experimental results and theoretical predictions have been attributed to the numerical models of quantum effects employed in Particle-In-Cell (PIC) codes used to simulate and analyse experiments.

A host of new experiments will begin this year, and will be able to probe the transition from classical to quantum physics in intense electromagnetic fields. It is therefore critical that we improve our understanding of theoretical models, and their implementations, in order to ensure that theoretical predictions and analyses keep up with experimental progress.

To meet this urgent experimental demand we propose developing existing theory on two fronts.

On one front, we will extend existing models to include currently neglected processes (such as absorption and trident pair production) in a systematic way that can be immediately employed by simulators. On the second front, we will analyse a number of quantum effects which cannot be captured by existing numerical models (but which become relevant in e.g. the overlapping field geometries of future facilities, or in dense electron bunches), assess their importance to experimental campaigns, and develop a methodology to implement them numerically, going beyond current models.

Doing so requires a team of researchers who are not only experts in the theory of quantum effects in intense laser physics, but who also have the experience required to understand numerical implementation and experimental analyses. This is not a case of benchmarking existing codes, already well-covered in the literature. What is needed, rather, is a "top down", approach which can verify, and improve upon, the models of quantum effects which are used in the codes.

Plymouth hosts an established, world-leading research group in the area of intense laser-matter interactions. Staff members are research-active and well-known in the community as experts in the theory of quantum effects in intense laser physics. Furthermore, the Investigators attached to this project are actively involved in experimental efforts, being for example part of the team which recently demonstrated radiation reaction in laser-matter collisions in an experiment at the UK's Central Laser Facility.

As such the Investigators have precisely the right skillset to undertake this timely project and deliver new results of import to a wide community of physicists. This will help maintain the UK's world-leading capabilities in the active research area of intense laser-matter interactions.

Researchers in a broad range of physics disciplines will benefit from the results of this programme, as one of our goals is to improve on existing widely used theoretical and numerical tools.

In terms of impact on research, our project will yield an explicit demonstration of what is and what is not included in current numerical models of intense laser-matter interactions. The results will further delineate the applicability of current methods, and will show us when and, importantly, how they must be improved. This will have an impact on a broad and active community of laser and plasma physicists. As it is critical to the analysis of experiments that theoretical models are well understood, this project will impact experimental collaborations and experiments to be performed on, for example, the UK's Astra-Gemini laser. The close connection of the PIs to active experimental groups in the UK will ensure that the results of the project reach experimentalists, and impact on the analysis of future experiments. (AI is involved in planning experiments with S. Mangles (Imperial) and C. Murphy (York), and BK is involved in planning experiments with G. Gregori (Oxford).)

In terms of impact on applications of intense lasers, the programme will lead to improved understanding of Compton sources, i.e. the generation of high frequency radiation by electrons colliding with laser fields. Moreover, having as a project milestone the inclusion of absorptive processes (such as pair-annihilation) into numerical codes, the programme will potentially develop a new branch of research into exotic gamma sources, generated by the manipulation of pair-plasmas using intense laser pulses. Such sources can be used to study biological samples and hence improve our ability to fight illness and disease, to perform nuclear resonance fluorescence imaging, which has applications in the nuclear reactor market, and is ideal for non-intrusive inspection, for example cargo scanning. Hence the improvements we will make to numerical models, used to interpret experimental results in this area, will have a broad long-term societal impact.

In terms of impact on the UK science base, the active area of intense laser physics will be strengthened by increasing the Host Organisation's research group size and output volume. The UK is at the forefront of high-intensity laser engineering, recently providing GBP 30 million of investiment in the European XFEL and, through the Centre for Advanced Laser Technology Applications (CALTA), providing technology for the Extreme Light Infrastructure and the Helmholtz International Beamline for Extreme Fields. Due to the involvement of the PIs in experimental campaigns at the CLF, an indirect economic benefit of the proposed research is the further promotion of high-intensity laser physics in the UK, completely in-line with the UK's technological portfolio.