Vacuum laser acceleration (VLA) of electrons has been an intense field of research for a long time due to the extremely high (>1 TV/m) accelerating fields. However, it is very challenging to realize and only a few promising experiments have been performed which have demonstrated the principle. Here, we report on the interaction of relativistic intensity (1020 Wcm-2) sub-two optical cycle (<5 fs) laser pulses with nanotips to realize and optimize VLA. Various properties of accelerated electrons (angular distribution, charge, and electron spectrum) are measured with different intensities and carrier envelope phases of the laser pulse. Among others, waveform dependence of the electron propagation direction is observed. Furthermore, comparable or even higher electron energies beyond 10 MeV are detected with lower laser intensity, i.e., longer focusing, than with high intensity. These surprising results are reproduced using particle-in-cell simulations, which indicate a nanophotonics electron emission from the nanotip followed by VLA. In fact, the unexpected observations are a direct proof of the VLA process and provide a way to optimize it towards higher energy, isolated, attosecond electron bunch generation.
The construction of 10 PW class laser facilities with unprecedented intensities has emphasized the need for a thorough understanding of the radiation reaction process. We describe simulations for a recent all-optical colliding pulse experiment, where a GeV scale electron bunch produced by a laser wakefield accelerator interacted with a counter-propagating laser pulse. In the rest frame of the electron bunch, the electric field of the laser pulse is increased by several orders of magnitude, approaching the Schwinger field and leading to substantial variation from the classical Landau-Lifshitz model. Our simulations show how the final electron and photon spectra may allow us to differentiate between stochastic and semi-classical models of radiation reaction, even when there is significant shot-to-shot variation in the experimental parameters. In particular, constraints are placed on the maximum energy spread and shot-to-shot variation permissible if a stochastic model is to be proven with confidence.
Electron-positron plasmas are a prominent feature of the high energy Universe. In the relativistic winds from
pulsars and black holes it is thought that non-linear quantum electrodynamics (QED) processes cause
electromagnetic energy to cascade into an e-e+ plasma. We show that next-generation 10PW lasers, available in
the next few years, will generate such a high density of pairs that they create a micro-laboratory for the first
experimental study of a similarly generated e-e+ plasma. In the first simulations of a 10PW laser striking a solid
we demonstrate the production of a pure electron-positron plasma of density 1026m-3. This is seven orders of magnitude denser than currently achievable in the laboratory and is comparable to the critical density for
commonly used lasers, marking a step change to collective e-e+ plasma behaviour. Furthermore, a new ultraefficient
laser-absorption mechanism converts 35% of the laser energy to a burst of gamma-rays of intensity
1022Wcm-2, potentially the most intense gamma-ray source available in the laboratory. This absorption results in a strong feedback between both pair and gamma-ray production and classical plasma physics leading to a new
physical regime of QED-plasma physics. In this new regime the standard particle-in-cell (PIC) simulation
approach, which has been the dominant kinetic simulation tool in plasma physics for 50 years, is inadequate. We
have developed a new approach (QED-PIC) which will provide a powerful new modelling tool essential to the
future advancement of the field of high intensity laser-plasma interactions.
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