Pair production in counter-propagating laser beams

Based on an analysis of a specific electron trajectory in counter-propagating beams, Bell and Kirk (2008 Phys. Rev. Lett. 101 200403) recently suggested that laboratory lasers may shortly be able to produce significant numbers of electron-positron pairs. We confirm their results using an improved treatment of non-linear Compton scattering in the laser beams. Implementing an algorithm that integrates classical electron trajectories, we then examine a wide range of laser pulse shapes and polarizations. We find that counter-propagating, linearly polarized beams, with either aligned or crossed orientation, are likely to initiate a pair avalanche at intensities of approximately 10(24) W cm(-2) per beam. The same result is found by modelling one of the beams as a wave reflected at the surface of an overdense solid.