Effect of laser-induced double-step ionization of a gas on vacuum electron acceleration

Abstract

The effect of laser-induced double ionization of a helium gas on electron acceleration is investigated. The optical field ionization of a gas of sufficient density can significantly change its refractive index, which makes the incident laser pulse diverge. For an enough laser intensity, the helium gas can be found doubly ionized and it strengthens the divergence of the pulse. As a result, electrons feel a very low laser intensity at the trailing part of the laser pulse. Hence, there is not much electron deceleration at the trailing part of the pulse. Therefore, a significant enhancement in electron energy by the laser acceleration may be observed.