Optimizing laser coupling, matter heating, and particle acceleration from solids using multiplexed ultraintense lasers

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

Theoretical Study of Laser Energy Absorption Towards Energetic Proton and Electron Sources

International audienceOur main goal is to describe and model the energy transfer from laser to particles, from the transparent to less transparent regime of laser-plasma interaction in the ultra-high intensity regime, and using the results obtained to optimize laser ion acceleration. We investigate the case of an ultra high intensity (10²² W/cm²) ultra short (20 fs) laser pulse interacting with a near-critical density plasma made of electrons and protons of density 5 n_{c} (where n_{c} = 1.1·10²¹ cm⁻³ is the critical density for a laser wavelength of 1 µm). Through 2D particle-in-cell (PIC) simulations, we study the optimal target thickness for the maximum conversion efficiency of the laser energy to particles. Theoretical modelling of the predominant laser-plasma interaction mechanisms predicts the particle energy and conversion efficiency optimization. Our studies led to an optimization of the target thickness for maximizing electron and proton acceleration

Numerical simulation of isotope production for positron emission tomography with laser-accelerated ions

International audienceThe experimental demonstration of laser acceleration of ions to multi-MeV energies with short, intense laser pulses has spurred the prospect of using this ion source for medical isotope production. Using numerical models for laser-plasma interaction and ion acceleration, then for ion transport and isotope production, we compute the isotope yields that could be expected from such sources, and their variations with interaction parameters such as target thickness and laser intensity. Using 36 fs, 4×10^20 W/cm^2 pulses at kilohertz repetition rate, more than 100 GBq of are expected after irradiation for 1 h

ASYMPTOTIC-PRESERVING SCHEME FOR THE FOKKER-PLANCK-LANDAU-MAXWELL SYSTEM IN THE QUASI-NEUTRAL REGIME.

This work deals with the numerical resolution of the Fokker-Planck-Maxwell system in the quasi-neutral regime. In this regime the sti ness of the stability constraints of classic schemes causes huge calculation times. That is why, we introduce a new stable numerical scheme consistent with the transitional and limit models. Such schemes are called Asymptotic-Preserving (AP) schemes in literature. This new scheme is able to handle the quasi-neutrality limit regime without any restrictions on time and space steps. This approach can be easily applied to angular moment models by using a moments extraction. Finally, two physically relevant numerical test cases are presented for the Asymptotic-Preserving scheme in di erent regimes. The rst one shows the e ciency of the Asymptotic-Preserving scheme in the quasi-neutral regime whereas the second one on the contrary corresponds to a regime where electromagnetic e ects are predominant

ASYMPTOTIC-PRESERVING SCHEME FOR THE FOKKER-PLANCK-LANDAU-MAXWELL SYSTEM IN THE QUASI-NEUTRAL REGIME.

This work deals with the numerical resolution of the Fokker-Planck-Maxwell system in the quasi-neutral regime. In this regime the sti ness of the stability constraints of classic schemes causes huge calculation times. That is why, we introduce a new stable numerical scheme consistent with the transitional and limit models. Such schemes are called Asymptotic-Preserving (AP) schemes in literature. This new scheme is able to handle the quasi-neutrality limit regime without any restrictions on time and space steps. This approach can be easily applied to angular moment models by using a moments extraction. Finally, two physically relevant numerical test cases are presented for the Asymptotic-Preserving scheme in di erent regimes. The rst one shows the e ciency of the Asymptotic-Preserving scheme in the quasi-neutral regime whereas the second one on the contrary corresponds to a regime where electromagnetic e ects are predominant

Proton acceleration mechanisms in high-intensity laser interaction with thin foils

International audienceThe interaction of short and intense laser pulses with plasmas or solids is a very efficient source of high-energy ions. This paper reports the detailed study, with particle-in-cell simulations, of the interaction of such a laser pulse with thin, dense targets, and the resulting proton acceleration. Depending on the laser intensity and pulse duration, the most energetic protons are found to come from the front, the core, or the back of the target. The main accelerating mechanisms discussed in this paper are plasma expansion acceleration, where proton acceleration is driven by the hot electron population, and shock acceleration, originating from the laser ponderomotive potential imposed at the front target surface. Three main regimes of proton acceleration are defined and the parameters for which each regime is dominant are obtained. For irradiances close to 10^20 W/cm^2, the highest proton energies are obtained from thin foils efficiently heated by relativistic transparency. At larger intensities, a complex interplay between collisionless shock acceleration and plasma expansion acceleration is evidenced