Luxe: combining high energy and intensity to spark the vacuum

The vacuum of quantum electrodynamics (QED) can be viewed as a medium akin to a dielectric which can be polarised by external fields. If these are sufficiently strong, the response of the vacuum becomes nonlinear and involves phenomena such as lightby- light scattering (‘nonlinear optics’) and, in extremis, ‘dielectric breakdown’, i.e. real pair production, if a critical field strength is exceeded. The LUXE experiment aims to realise near-critical fields through collisions of photons stemming from an ultra-intense optical laser with high energy electrons or photons provided by the European XFEL linear accelerator. This set-up provides a golden opportunity to enter the uncharted territory of strong-field quantum electrodynamics in the non-perturbative regime.