Nonlinear quantum electrodynamics in the focus of a high peak power laser

We have constructed a Λ=1.053 μm laser system which delivers 2J, 1.5 ps pulses, focused down to a 1.4 times diffraction limited, 50 μm² spot size. When 46.6 GeV electrons are brought into approximately head-on collision with a laser pulse at the Stanford Linear Accelerator Center, they see, in their own rest frame, a Lorentz transformed intensity. In such circumstances, multiphoton Compton scattering up to at least fourth order has been observed, and a limit for multiphoton Breit-Wheeler pair production has been established