The intensity dependent mass shift: existence, universality and   detection
  The electron mass shift in a laser field has long remained an elusive concept. We show that the mass shift can exist in pulses but that it is neither unique nor universal: it can be reduced by pulse shaping. We show also that the detection of mass shift effects in laser-particle scattering experiments is feasible with current technology, even allowing for the transverse structure of realistic beams. 
Chris Harvey, Thomas Heinzl, Anton Ilderton, Mattias Marklund
hep-ph physics.atom-ph