  Since the invention of chirped pulse amplification, which was recognized by a
Nobel prize in physics in 2018, there has been a continuing increase in
available laser intensity. Combined with advances in our understanding of the
kinetics of relativistic plasma, studies of laser-plasma interactions are
entering a new regime where the physics of relativistic plasmas is strongly
affected by strong-field quantum electrodynamics (QED) processes, including
hard photon emission and electron-positron ($e^+$-$e^-$) pair production. This
coupling of quantum emission processes and relativistic collective particle
dynamics can result in dramatically new plasma physics phenomena, such as the
generation of dense $e^+$-$e^-$ pair plasma from near vacuum, complete laser
energy absorption by QED processes or the stopping of an ultrarelativistic
electron beam, which could penetrate a cm of lead, by a hair's breadth of laser
light. In addition to being of fundamental interest, it is crucial to study
this new regime to understand the next generation of ultra-high intensity
laser-matter experiments and their resulting applications, such as high energy
ion, electron, positron, and photon sources for fundamental physics studies,
medical radiotherapy, and next generation radiography for homeland security and
industry.
