Extreme Light and Quantum Fields

2015 is the International Year of Light, and of its purposes is “to raise
awareness of optical technologies”. One such technology, high-power
lasers of the petawatt class and beyond, provides the most intense light sources created by humankind so far. The intensities and field
strengths in question are in excess of 1022 W/cm2 and 1014 V/m, respectively
magnitudes that correspond to concentrating the total solar
radiation on a pinhead. This talk will present an overview of the uses
and consequences of such extreme environments within the realm of
particle physics. The relevant theory is strong-field QED, with the
laser beams providing a rather peculiar electromagnetic background
field. The magnitudes above are such that a nonperturbative treatment
of the background becomes a necessity. Using appropriate theoretical
tools, a number of phenomena will be addressed, including
radiation reaction, nonlinear Thomson/Compton scattering, laserstimulated
pair production and photon-photon scattering. A particular
incarnation of the latter, polarisation flip forward scattering,
or vacuum birefringence, will be discussed in some detail, with an
outlook on a planned experiment at the European XFEL at DESY.