Free wave laser acceleration of electrons and consequences for the Umstadter experiment

Abstract

In contrast to electron acceleration by lasers due to plasma effects (beat wave etc.) the laser acceleration of electrons in vacuum (free wave accelerator) has been established as a pure Lorentz force mechanism. This indeed leads to the same acceleration as the pondermotive potential though it is mainly based on an incomplete phase description of the quiver motion and on general phase-, intensity- and exact field-conditions of the complete theory. It is remarkable that the result of the Umstadter experiment producing 108 30 MeV-electrons within a cone of 14 degrees of the beam direction by firing a 25 TW-400-fs Nd-glass laser pulse on a gas puff can be reproduced completely. The theory of the free wave acceleration yields the same electron number as measured. A similar cone angle and an electron energy of 30 MeV if the longitudinal optical field is included while the purely transveral field arrives at 60% higher energies. For the 2 PW pulses we expect 300 MeV electron energy and a cone angle of 5 degrees....