Laser-induced acceleration of Helium ions from unpolarized gas jets

Abstract

In order to develop a laser-driven spin-polarized 3He-ion beam source available for nuclear-physics experiments as well as for the investigation of polarized nuclear fusion, several challenges have to be overcome. Apart from the provision of a properly polarized 3He gas-jet target, one of the biggest milestones is the demonstration of the general feasibility of laser-induced ion acceleration out of gas-jet targets. Of particular importance is the knowledge about the main ion-emission angles as well as the achievable ion-energy spectra (dependent on the optimal set of laser and target parameters). We report on the results of such a feasibility study performed at PHELIX, GSI Darmstadt. Both 3He- and 4He-gas jets (n_gas ∼ 10^19 cm−3) were illuminated with high-intensity laser pulses, I_L ~ O(10^19 W cm^-2). The main ion-emission angles could be identified (±90° with respect to the laser-propagation direction) and the ion-energy spectra for all ion species could be extracted: for the optimal laser and target parameters, the high-energy cut-offs for He^2+,1+ ions were 4.65 MeV (with a normalized energy uncertainty of Delta E E^-1 = 0.033) and 3.27 MeV (Delta E E^-1 = 0.055), respectively