Vacuum polarisation effects in intense laser fields

Polarisation of the vacuum by an external electromagnetic field is predicted to lead to an array of non-linear processes. In light of upcoming laser facilities that will access intensity ranges orders of magnitude above current limits, the continued study of vacuum polarisation effects is both necessary and timely. By considering how photons from a probe laser field are scattered by two ultra-intense laser beams, we present a novel experimental scenario in which interference effects separate the vacuum signal from the probe background. By placing emphasis on experimental considerations, we demonstrate a realistic arrangement that could be used to observe, for the first time, real, elastic, photon-photon collisions. In doing so, we also show how strong-field lasers can in principle be used to generate a double-slit experiment consisting entirely of light. Moreover, such a set-up is also shown to modestly increase vacuum birefringence and dichroism over traditional two-beam collisions. We complement this by expounding an original theoretical method that incorporates both finite temperature and vacuum polarisation in a common setting. By employing this method on the case of a constant crossed field, we calculate the resulting change in the pressure of the vacuum in an external field