The proposal is to explore the potential of using a fully ionised gas or plasma as an efficient short pulse amplifier. By exciting a plasma wave by two colliding (seed and pump respectively) pulses in plasma, it is possible to amplify the short seed pulse efficiently. The bandwidth of the plasma amplifier medium is enhanced when a chirped pump pulse is utilised. In the linear regime, before saturation of the amplifying process takes over, the long chirped pump laser pulse provides distributed amplification where different spectral components of the seed are amplified at different longitudinal positions in the plasma through the creation of a chirped plasma density echelon, much like a diffraction grating. This behaves as a long chirped mirror which simultaneously backscatters and compresses the chirped pump pulse and effectively broadens the gain bandwidth to that of the pump. The gain and the bandwidth of the amplifier depend on the natural oscillation frequency of the plasma (the plasma frequency) and the chirp rate (the rate at which the frequency changes along the pump pulse) and spectral bandwidth of the pump. This contrasts with conventional chirped pulse amplifiers (CPAs) and optical parametric chirped pulse amplifiers (OPCPAs) where the probe is chirped while the pump is usually monochromatic (un-chirped). The chirped pulse Raman amplifier has potential use either as a high fidelity ultra-short pulse high power linear amplifier or as a compressor of high energy chirped pulses from a conventional CPA amplifier. It also avoids the requirement for extremely large and expensive optical elements and compressors in vast vacuum chambers. Furthermore, because chirped pulse Raman amplification is a three wave parametric interaction it provides a means of eliminating pre-pulses and pedestals which usually limit the usefulness of conventional solid state CPA amplifiers. This research proposal will investigate the linear and non-linear stages of Raman amplification with a view to develop extremely high power lasers which have the potential of opening up new frontiers of physics such as using lasers to create particles from vacuum or create astrophysical conditions in the laboratory.

A common perception is that laboratory tests of fundamental physics necessarily require large particle colliders. However, thanks to the development of ultra high-intensity optical lasers and 4th generation light sources, new approaches are now possible that exploit the simultaneous interactions of multiple photons with matter and vacua via quantum field fluctuations. In this proposal, we will employ these high-field non-perturbative quantum optics processes to search for new fundamental particles. Since accelerator-based searches have not yet found new physics at high energies, ultra high-intensity optical lasers and 4th generation light sources offer a novel complementary approach for searches at optical and X-ray energies. This proposal addresses an important question in fundamental physics by developing a laboratory search for new particles beyond the Standard Model called axions. Our work will be able to probe axion masses bigger than a few eV up to a keV - a region that is currently inaccessible to laboratory searches. In the eV-keV mass range. the searches proposed here are the only model-independent ones, meaning that the experiments have full control over both the production and reconversion of axions within the same apparatus - without the need to assume that axions are produced by astrophysical objects (such as the Sun) or constitute a large fraction of the dark matter.

We propose to build on the successes of the ALPHA-X project with a new programme of research to investigate and develop novel compact radiation sources that explicitly exploit laser-driven plasma waves. The project will take forward the development of wakefield accelerators and utilise the sub-10 fs electron bunches accelerated in plasma channels to produce ultra-short pulses of coherent infrared to x-ray radiation in a FEL and coherent radiator structures. The main objective will be to push towards hard x-rays and gamma rays by utilising the very short spatial period undulator-like structures of plasma waves to lay down the foundations of sources in a spectral region hitherto not accessible. We will also push the frontiers of ultra-short pulse generation by: i) controlling and reducing the electron bunch duration from wakefield accelerators using pre-bunching techniques, which will also increase the peak current available while reducing the pulse length from a radiation source, and by ii) investigating the generation and tailoring of arbitrary shaped single-cycle pulses (initially in the visible) by backscattering tailored terahertz pulses from relativistic mirrors formed by relativistic plasma wakes and ionisation fronts. The experimental programme to develop these novel compact radiation sources will utilise the unique facilities at Strathclyde, set up under the ALPHA-X project, and resources available in the EU, US and China, to provide a mix of long-term development programmes and short-term (6-week) campaigns that take advantage of the particular laser beam characteristics available at the facilities. An important aspect of the project will be a substantial theoretical programme that will be undertaken by an established team of theoreticians that has previously worked together under ALPHA-X, and new teams that bring new approaches and backgrounds to bear on the significant theoretical challenges. The large group of collaborators provide both breadth and depth to the programme, and through their contributions and access to their various facilities, will also enable very effective use of resources. The programme of research is central to a UK roadmap that outlines potential new landscapes and ways forward in the field.

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.

Rising greenhouse gas (GHG) emissions are creating a serious threat to our planet, through their key impact of increasing temperatures. The 2015 Paris climate agreement, signed by 195 countries under the United Nations Framework Convention on Climate Change (UNFCCC), pledges to hold global average temperature increases to 2 'C above pre-industrial levels (c.1750). For context, in 2015, we passed the 1'C rise mark, and most climate models forecast a 2-4'C temperature rise by 2100, unless real actions are taken to reduce GHG emissions. In short, the situation is serious, and the window for staying within the 2'C target is closing. To reduce GHG emissions, a key part of government policy is to reduce the amount of energy we use. This is because most of our energy come from fossil fuels (i.e. oil, coal, gas), and burning them causes around 75% of the world's GHG emissions. The main policy for reducing energy use has been introducing energy efficient technologies, i.e. more efficient cars, lighting and heating systems. However, a key problem exists: to date energy efficiency has not reduced total energy consumption: in fact energy use globally is still rising, slightly behind economic output (Gross Domestic Product, GDP). Thus energy use and GDP have remained linked, or 'coupled' together. So a key question for the UK (and globally) is to work out exactly how to decouple energy-GDP: i.e. reduce energy use but allow economic growth. Studying the energy-GDP decoupling problem is the key aim of my research. Given the short time to reduce GHG emissions, we need to look at this problem from as many different angles as possible. This is where my research fits in: I work in an area of research that provides a different approach to looking at this problem compared to the mainstream (i.e. most common) methods. My research uses 'exergy analysis' to study the thermodynamic efficiency of energy use in a whole economy. Exergy is energy that is 'available for work'. Taking an example to illustrate exergy: though water in a hydroelectric dam has 'potential energy', it only becomes 'available for work' if there is a difference in water level between the two sides of the dam. If one side is 150m higher than the other, then physical 'work' (in this case hydroelectricity) can be extracted, but not if both water levels are 150m high. By studying how much energy is available for work as 'exergy' in an economy (for end uses such as transport, industrial machines, heating, cooling, lighting), we can calculate how (thermodynamically) energy efficient the whole economy is. This thermodynamic measure of energy efficiency (called exergy efficiency) can give us new insights into how much energy we are actually saving, versus how much we think we are going to save. This difference also tells us how much energy 'rebound' we have, i.e. the energy that is taken back by the economy. A better understanding of the size and role of these two factors - energy efficiency and energy rebound - holds the key to unpicking the energy-GDP decoupling puzzle. This is what my research sets out to achieve. The research is a five year project, based at the University of Leeds, where I will work with a 4 year PhD researcher and 3 year postdoctoral researcher, and other researchers who will contribute part time expertise. Our research in planned in three parts, 1. we will develop national exergy datasets into a global database, which 2. we will use to identify new insights and links of the key factors (energy efficiency and energy rebound) in the energy-GDP relationship, which lastly 3. will be used to test policies for achieving energy-GDP decoupling. We have several project partners outside of the University of Leeds, who we will work together with on sub-projects: The Bank of England; the UK Department for Business, Energy and Industrial Strategy (BEIS); Calvin College (USA) and Instituto Superior Técnico (Portugal). A steering group will provide advice during the project.