Collimated ion beam by a laser-illuminated tailored target

Suppression of transverse proton beam divergence is demonstrated by a tailored thin foil target with a hole at the opposite side of laser illumination. When an intense short pulse laser illuminates the thin foil target with the hole, transverse edge effects of an accelerated electron cloud and an ion cloud are eliminated by a protuberant part of the hole: the edge effects of the electron cloud and the ion cloud induce the proton beam divergence. Therefore the transverse proton beam divergence is suppressed well. Firstly this paper presents the robustness of the hole target against laser parameter changes in a laser spot size and in a laser pulse length, and against a contaminated proton source layer. It may be also difficult to make the laser axis coincide with the target hole-center line in realistic experiments and uses, when the target has only one hole. 2.5-dimensional PIC (particle-in-cell) simulations also present that a multiple-hole target is robust against the laser alignment error and the target positioning error. The multi-hole target may serve a robust target for practical uses to produce a collimated proton beam.