Generation of sub-picosecond GeV electron bunches by laser acceleration in vacuum

The interaction of free electrons with intense laser beams in vacuum was studied using 3D test particle simulation instead of solving analytically the relativistic Newton-Lorentz equation of motions. We found a group of solutions of the equation which show very interesting and unusual characteristics. When the laser intensity is strong enough a0 ≥100, where a0 ≡ eE0 / meωc is a measure of the laser intensity, an electron can be captured into the high-intensity region and accelerated to GeV energy with acceleration gradient of tens of GeV/cm. The accelerated GeV electron bunch is a macro-pulse composed of a lot of micro-pulses. The paraxial approximation equations of the Gaussian laser beam used in the simulation are of high accuracy and the contribution of the high-order correction is almost negligible when the laser beam width w0 ≥ 60.