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A great deal was accomplished during the first year of the project.
*Challenges and results achieved*
1. One of the main challenges the project sought to address was that of going beyond the `plane wave' approximation. This is the assumption that the fields of an intense laser may be modelled as a plane wave; this is a simplistic field model which does not encompass the tight spatial focussing of high intensity laser pulses and the effects on particle interactions due to it. It has been recognised recently that there are many situations in which this model fails to capture the relevant physics.
A new framework for the investigation of laser-matter interactions beyond the plane wave model was established early in the project. This was an interdisciplinary work which brought results from the mathematical community (on `superintegrability') to bear on the physics problem. The paper was published in Physical Review Letters and selected as an ""Editors' choice"" for its interdisciplinary nature and potential impact. A paper presenting related results to the mathematical physics community was published in J.Phys.A.
2. In pursuit of experimental signatures of quantum effects we identified a new, observable manifestation of quantum physics in laser-matter collisions. We dubbed this effect ``quenching'' in analogy to fluorescence quenching in chemistry; it is a suppression of radiative losses due to quantum effects which can could be observed in the interaction of energetic particles with short laser pulses. These results were published in Physical Review Letters.
3. Around six months into the project our collaboration completed the analysis of an experiment performed on the Gemini laser in the UK. We have made the first experimental observation of radiation reaction in laser-particle collisions. This paper, essentially the first of its kind, signals the start of a new era of laser experiments and is expected to generate quite some interest in the community. The paper is available on the arXiv preprint server and is under review in Physical Review X.
4. Combining analytic and numerical results, we were able to show how to create an ultra-bright GeV photon source at next-generation laser facilities. The source concept represents the state of the art, and was published in Physical Review X.
5. Toward the end of the first year, a second new framework was developed for investigations of laser-matter interactions beyond the background field approximation. This represents a second significant step forward, allowing theorists to include the hitherto-neglected effects of depletion in back reaction. Importantly, we were able to show how to include these effects within an already well-established theoretical formalism, making our methods and results immediately accessible to other researchers int the field. The paper has been accepted for publication in Physical Review D.
*Dissemination*
1. A twitter account attached to the project was set up to advertise results and make other researchers aware of the project.
2. University press releases were organised to announce publications in high-impact journals such as Physical Review Letters and Physical Review X, and to promote the action at the Faculty and University level. These press releases were also recirculated on twitter in order to reach the research community.
3. The results of the project have been presented at several leading conferences:
ILNPC 2017 in Yokohama, Japan
The UK High Power Laser annual meeting, Oxford, UK
ExHILP 2017 Lisbon, Portugal
4. The researcher was invited to visit ELI-NP, a next-generation EU infrastructure-roadmap-funded laser facility, in order to discuss possible future experiments. Positive interactions between the researcher and ELI-NP led to a standing invitation to lecture at the ELI-NP summer school.
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