Effect of polarization on the structure of electromagnetic field and   spatiotemporal distribution of $e^+e^-$ pairs by colliding laser pulses
  Electron-positron pair production by means of vacuum polarization in the presence of strong electromagnetic (EM) field of two counterpropagating laser pulses is studied. A 3-dimensional model of the focused laser pulses based on the solution of the Maxwell's equations proposed by Narozhny and Fofanov is used to find the structure of EM field of the circularly polarized counterpropagating pulses. Analytical calculations show that the electric and magnetic fields are almost parallel to each other in the focal region when pulses are completely transverse either in electric (e-wave) or magnetic (h-wave) field. On the other hand the electric and magnetic fields are almost orthogonal when the counterpropagating pulses are made up of equal mixture of e- and h- polarized waves. It is found that while the latter configuration of the colliding pulses has much larger threshold for pair production it can provide much shorter electron/positron pulses compared to the former case. The dependence of pair production and its spatiotemporal distribution on polarization of the laser pulses is analyzed using the structure of the EM field. 
Chitradip Banerjee, Manoranjan P. Singh
physics.plasm-ph