  In this work we study the production of electron-positron pairs from vacuum
in presence of a field resulting from the collision of two counter-propagating
FEL beams that undergo Gaussian amplitude fluctuations. Our work aims to the
extension of previous works based on the standing wave hypothesis, by including
the inherent stochastic amplitude fluctuations of the individual FEL beams. As
shown, depending on the order of the process, a large non-linear enhancement in
the number of created pairs can be expected over a big intensity window in the
multi-photon regime. Vacuum pair creation in view of future plans on the
production of ultra-strong and high energy radiation in FEL facilities is also
discussed.
