Strong field effects in laser pulses: The Wigner formalism

We investigate strong field vacuum effects using a phase-space approach based on the Wigner formalism. We calculate the Wigner function in a strong null-field background exactly, using lightfront field theory. The Wigner function exhibits the distinct features of strong field QED: in particular, we identify the effective mass in a laser pulse, compare it to the well-known mass shift in a periodic plane wave and identify signals of multiphoton absorption and emission. Finally, we show how to extend our results to describe vacuum pair production in colliding laser pulses.