Boosted acceleration of protons by tailored ultra-thin foil targets

Vural Kaymak,Alexander Pukhov,Esin Aktan,Marc Papenheim,Mirela Cerchez,Oswald Willi,Rajendra Prasad,Bastian Aurand,Bentsian Elkin,Hella-C Scheer,Anna-Marie Schroer

doi:10.1038/s41598-019-55011-2

Abstract

We report on a detailed experimental and numerical study on the boosted acceleration of protons from ultra-thin hemispherical targets utilizing multi-Joule short-pulse laser-systems. For a laser intensity of 1 × 1020 W/cm2 and an on-target energy of only 1.3 J with this setup a proton cut-off energy of 8.5 MeV was achieved, which is a factor of 1.8 higher compared to a flat foil target of the same thickness. While a boost of the acceleration process by additionally injected electrons was observed for sophisticated targets at high-energy laser-systems before, our studies reveal that the process can be utilized over at least two orders of magnitude in intensity and is therefore suitable for a large number of nowadays existing laser-systems. We retrieved a cut-off energy of about 6.5 MeV of proton energy per Joule of incident laser energy, which is a noticeable enhancement with respect to previous results employing this mechanism. The approach presented here has the advantage of using structure-wise simple targets and being sustainable for numerous applications and high repetition rate demands at the same time.

Highlights

We report on a detailed experimental and numerical study on the boosted acceleration of protons from ultra-thin hemispherical targets utilizing multi-Joule short-pulse laser-systems
While the fundamental radiation pressure acceleration (RPA) process benefits from the use of circular polarized light[18], it was demonstrated that the use of a linear polarized light at high intensities leads to a hybrid acceleration regime, in which target normal sheath acceleration (TNSA) and RPA coexist[19,20,21]
We report for the first time in a detailed experimental and numerical study using a combination of an ultra-thin and tailored target, irradiated by a linearly polarized femtosecond laser pulse at an intensity of 1 × 1020 W/cm[2]

Summary

Introduction

We report on a detailed experimental and numerical study on the boosted acceleration of protons from ultra-thin hemispherical targets utilizing multi-Joule short-pulse laser-systems. Investigations have addressed, among others, the influence of the target thickness[12], laser pulse duration[13] and plasma gradients[14] Another extensively studied subject is the modification of the target using different methods, in order to obtain an increase of the hot electron sheath population responsible for the accelerating TNSA field. A different route to reach higher particle energies is the use of acceleration schemes like radiation pressure acceleration (RPA)[15,16] This attracted attention due to the promising properties such as a proton cut-off energy scaling of Ecutoff;RPA ∝ I010 and its expected high energy conversion efficiency at ultra-relativistic intensities[17]. The initial laser contrast, which is better than 1:10−8 at 80 ps before the main pulse, is further enhanced by another three orders of magnitude using a single plasma mirror based on the design of ref

Methods

Results

Conclusion