Orateur
Description
The interaction of an ultra-intense (>$10^{18}$ W/cm$^2$) laser pulse with a suitable target can result in the acceleration of particles, like protons, and the generation of secondary radiation, like high-energy photons and positrons. Concerning solid targets, the Target Normal Sheath Acceleration (TNSA) [1] is surely the most assessed configuration to accelerate the protons naturally present as impurities on the target surface. To optimise the process, non-conventional targets capable of increasing laser-matter coupling have been developed. One can achieve this goal by growing on top of a solid metallic film a nanostructured foam having an average density in the near-critical regime for the laser [2]. This configuration is referred to as Double Layer Target (DLT). Experimental campaigns confirmed the enhancement of the energy of the protons generated with DLTs when comparing them to conventional targets [3]. Moreover, numerical studies have proposed such a configuration to efficiently generate high-energy (MeV) photons via Non-Linear Inverse Compton Scattering (NICS) [4] and these photons could initiate pair production via the non-linear Breit-Wheeler process during the interaction itself. Particle in-cell (PIC) tools are amongst the most assessed methods to study the interaction of a laser with a target and their integration with Monte Carlo (MC) modules allows accounting for ionisation, photon generation, pair production and collisions. The open-source PIC code SMILEI [5] offers the possibility both to integrate the foam nanostructure using external files and to use some specific MC modules to account for all the aforementioned processes. This contribution aims to present the results of simulations performed in SMILEI of different possible uses of DLTs. The study of the interaction of different TW-class lasers with DLTs is first presented to evaluate their exploitation as compact proton sources. The relatively low intensity of such lasers raises the relevance of the effects of the nanostructure of the foams [6] and of the ionisation processes in laser propagation. A campaign of 2D and 3D simulations to study these effects was performed. The results show that the DLTs are effective in increasing and optimising the maximum energy of the protons (achieving tens of MeV for tens of TW lasers or activating the acceleration for sub-TW ones) and that the ionisation process becomes influential when the laser intensity is relatively low. Secondly, the use of TW/PW-class lasers as sources of high-energy photons and for pair production is considered. Our results show the relevance of DLTs for efficient photon and pair production and the possibility to optimise these processes acting on target parameters like foam density and thickness and solid layer composition.
[1] M. Passoni et al 2010 New J. Phys. 12 045012
[2] M Passoni et al 2020 Plasma Phys. Control. Fusion 62 014022
[3] M. Passoni et al. 2016 Phys. Rev. Accel. Beams 19 061301
[4] M. Galbiati et al. 2023 Front. Phys. 11 1117543
[5] J. Derouillat et al. 2018 Comput. Phys. Commun. 222 351-373
[6] L. Fedeli et al. 2018 Sci. Rep. 8 3834
