Muon pair creation by two x-ray laser photons in the field of an atomic   nucleus
  The generation of muon-antimuon pairs is calculated in the collision of an ultrarelativistic bare ion with an intense x-ray laser beam. The reaction proceeds nonlinearly via absorption of two laser photons. By systematic study throughout the nuclear chart we show that the interplay between the nuclear charge and size, along with the possibility of nuclear excitation leads to saturation of the total production rates for high-Z ions, in contrast to the usual Z^2 scaling for pointlike projectiles. The process is experimentally accessible by combining present-day ion accelerators with near-future laser sources and in principle allows for the measurement of nuclear form factors. 
Carsten M\"uller, Carlus Deneke, Christoph H. Keitel