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Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations. Here, we investigate how to optimize their coupling with solid targets. Experimentally, we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside. The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations, revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection, which is one possible mechanism to boost electron energization. In addition, the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation. Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams.

Abstract 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.