Electron acceleration in vacuum by ultrashort and tightly focused   radially polarized laser pulses
  Exact closed-form solutions to Maxwell's equations are used to investigate electron acceleration driven by radially polarized laser beams in the nonparaxial and ultrashort pulse regime. Besides allowing for higher energy gains, such beams could generate synchronized counterpropagating electron bunches. 
Vincent Marceau, Alexandre April, and Michel Pich\'e
physics.acc-ph physics.optics