Pair production at high laser intensity? 
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*Using high laser intensity to produce electron-positron pair, is it still required interaction with nucleus as is the case when gamma rays are used?

*What causes the pair creation ? 
 A: I had not realized this had been happening, very interesting.
Hand waving: when the intensity of the laser is high enough electrons can be accelerated to relativistic energies and create e+e- pairs interacting with the collective electric and magnetic fields of the laser pulse.
Here is a link to search for  calculations  , (first in list)  .
Electrons have to be supplied from the atoms of a gas on which the laser is shining. The interaction is a collective field one with the electron, in these calculations, not with the nucleus.
And another using quantum electrodynamics:

Production of electron-positron pairs from vacuum in the combined electromagnetic fields of a high-intensity laser pulse and an atomic nucleus is studied within the framework of laser-dressed quantum electrodynamics. The focus lies on the influence exerted by a finite laser pulse length on the energy spectra of created electrons and positrons, which is examined in a broad range of field frequencies and intensities. The results for an isolated short laser pulse are also compared with corresponding calculations for an infinite train of laser pulses. It is shown that the laser pulse length and its carrier-envelope phase have a substantial effect on the pair creation process, leading to both quantitative and qualitative differences in the particle spectra.

It is behind a pay wall so I cannot see what "atomic nucleus" means in this case. Certainly the diagrams will be different than the gamma-nucleus diagrams.
