Nonperturbative Bethe-Heitler pair creation in combined high- and   low-frequency laser fields
  The nonperturbative regime of electron-positron pair creation by a relativistic proton beam colliding with a highly intense bichromatic laser field is studied. The laser wave is composed of a strong low-frequency and a weak high-frequency mode, with mutually orthogonal polarization vectors. We show that the presence of the high-frequency field component can strongly enhance the pair-creation rate. Besides, a characteristic influence of the high-frequency mode on the angular and energy distributions of the created particles is demonstrated, both in the nuclear rest frame and the laboratory frame. 
Sven Augustin, Carsten M\"uller
hep-ph physics.atom-ph