Positron–hydrogen ionizing collisions in the presence of a laser field

Abstract

Triple differential cross sections (TDC) for positron–hydrogen ionization in the presence of a laser field are derived within a treatment which uses the Coulomb–Born wave approximation. The laser field is treated classically in the dipole approximation and taken to be homogeneous and single mode. Calculations are specialized to the case of a coplanar asymmetric geometry. The presence of the laser is found to alter significantly the shape of the angular distribution of the ejected electrons when photon exchanges occur. Laser electric fields parallel to the positron transferred momentum [Formula: see text] increase the number of electrons ejected in the forward direction, compared to the no-field case. Laser electric fields perpendicular to Kif double the peaks present in the field-free angular distribution and rotate them symmetrically in opposite directions from the Kif axis towards the EL axis. The results for ionization by positrons are compared to those for ionization by electrons (within the same theoretical treatment). Differences are found only for [Formula: see text]. The limits of validity of the model are discussed, together with simple physical arguments to explain the modifications to the shape of the TDC.