Narrow-band acceleration of gold ions to GeV energies from ultra-thin foils

Interaction of intense lasers with nm thick targets provides an attractive regime for the acceleration of ions of all types. Acceleration of heavy ions however is undermined in the presence of low charge contaminant species due to their higher charge-to-mass ratio. Here we show narrow-band acceleration of very heavy Au ions from ~15 nm Au foils driven by a sub-Petawatt laser, with spectral peaks of 1.5 ± 0.5 GeV at fluxes on the order of 1012 particles per steradian. 3D and 2D particle-in-cell simulations show a complex interplay between different acceleration mechanisms at different stages of the interaction, suggesting the spectrally peaked Au ion bunches stem from strong radiation pressure acceleration on a heavy-ion dominant plasma in the moments just before transparency, followed by an efficient acceleration due to transparency-enhanced mechanisms. Acceleration of heavy ions is difficult in presence of low charge contaminants due to their high charge-to-mass ratio. The authors use ultra-thin Au foils to efficiently accelerate both contaminants and heavy ions, discussing the interplay between distinct acceleration mechanisms at different stages of interaction via particle-in-cell simulations.