Laser-driven proton acceleration from ultrathin foils with nanoholes

Giada Cantono,Evgeniya Smetanina,Alexandre Dmitriev,Julien Ferri,Claes-Göran Wahlström,Anders Persson,Tünde Fülöp,Alexander Permogorov

doi:10.1038/s41598-021-84264-z

Giada Cantono, Evgeniya Smetanina + Show 6 more

Open Access

https://doi.org/10.1038/s41598-021-84264-z

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Abstract

Structured solid targets are widely investigated to increase the energy absorption of high-power laser pulses so as to achieve efficient ion acceleration. Here we report the first experimental study of the maximum energy of proton beams accelerated from sub-micrometric foils perforated with holes of nanometric size. By showing the lack of energy enhancement in comparison to standard flat foils, our results suggest that the high contrast routinely achieved with a double plasma mirror does not prevent damaging of the nanostructures prior to the main interaction. Particle-in-cell simulations support that even a short scale length plasma, formed in the last hundreds of femtoseconds before the peak of an ultrashort laser pulse, fills the holes and hinders enhanced electron heating. Our findings reinforce the need for improved laser contrast, as well as for accurate control and diagnostics of on-target plasma formation.

Highlights

Structured solid targets are widely investigated to increase the energy absorption of high-power laser pulses so as to achieve efficient ion acceleration
We investigated the maximum energy of proton beams accelerated from flat foils of gold, perforated with a non-periodic distribution of nanometric holes
Observing the cutoff energies of the protons accelerated in the BWD direction is a standard procedure to ensure that the laser contrast is high enough to prevent plasma formation on the target surface, as a step-like density profile enables efficient laser absorption through the vacuum-heating m echanism[33,34] and the establishment of the Target normal sheath acceleration (TNSA)-driving fields on the front side of the target

Summary

Introduction

Structured solid targets are widely investigated to increase the energy absorption of high-power laser pulses so as to achieve efficient ion acceleration. Increasing the energy transfer from the laser pulse to the hot electrons that develop the accelerating sheath field (i.e. increasing the absorption) results in larger yields and energies for the TNSA-driven ion beams To this aim, a well-established strategy consists of adding micro- and nanostructures on the front surface of the target[4]. Faced with similar laser-to-proton energy conversion efficiencies, crucial aspects in the choice of the most efficient nanostructures become the costs of manufacturing and handling, which in turn depend on how stringent the geometrical constraints are[7,11,22] In this context, we investigated the maximum energy of proton beams accelerated from flat foils of gold, perforated with a non-periodic distribution of nanometric holes (nanoholes, NHs). With a greater number of highly energetic electrons crossing the target, enhancement factors of the maximum proton energy between 1.4 and 2 were reported for a variety of NH parameters[26]

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