Non-linear pair production in scattering of photons on ultra-short laser pulses at high energy

We consider scattering of a photon on a short intense laser pulse at high energy We argue that for ultra-short laser pulses the interaction is coherent over the entire length of the Pulse At low pulse intensity I the total cross section for electron-positron pair production is proportional to I However, at pulse intensities higher than the characteristic value I(s), the total cross section saturates - it becomes proportional to the logarithm of intensity This non-linear effect is due to multi-photon interactions We derive the total cross section for pair production at high energies by resuming the multi-photon amplitudes to all orders in intensity. We calculate the saturation intensity I(s) and show that it is significantly lower than the Schwinger's critical value We discuss possible experimental tests (C) 2010 Elsevier B.V All rights reserved