Modeling and simulations of ultra-intense laser-driven bremsstrahlung with double-layer targets

Abstract

High-energy bremsstrahlung emission can occur owing to electron scattering in the nuclei or ions Coulomb field following the relativistic-electron generation in high-intensity laser interaction with plasmas. Such emission of photons in the keV-MeV energy range is of interest to characterize the relativistic electron populations and develop laser-based photons sources. Even if it is a well-established and widely studied emission process, its modeling in laser-plasma scenarios needs further investigation. Moreover, advanced near-critical double-layer targets (DLTs), consisting in a low-density foam deposited on a thin solid substrate, have never been explored extensively for bremsstrahlung photon emission. Therefore, in this paper, we show the rationale, advantages, limitations, application regime, and complementarity of different modeling approaches and apply them to the unconventional configuration based on DLTs. We couple multi-dimensional particle-in-cell simulations with a Monte Carlo strategy to simulate bremsstrahlung in two ways: integrated into the particle-in-cell loop itself or after the simulation with two separate codes. We also use simplified semi-analytical relations to retrieve the photon properties starting only from information on the relativistic electrons. With these tools, we investigate bremsstrahlung emission when an ultra-intense laser (0.8 μm wavelength, 30 fs duration, a0=20 and 3 μm waist) interacts with DLTs having different properties. Despite some limitations of the numerical tools, we find that all approaches significantly agree on the characteristics of ∽1-100 MeV photon emission. This points to the possibility of adopting the different modeling approaches in a complementary way while at the same time identifying the best suited for a specific scenario. Regardless, DLTs appear to overall boost the high energy photon emission while at the same time enabling control of the emission itself.

Numerical investigation of non-linear inverse Compton scattering in double-layer targets

“…Consequently, as demonstrated in [44], DLTs could become interesting for electronpositron pair generation at extreme intensities (~10 23 W/cm 2 ). At the same time, by choosing a micrometric DLT with low-Z layers, we can focus on NICS also in non-extreme regimes of laser-plasma interaction (a 0 ~20-60) since bremsstrahlung production yield has proven to be low in this case [45,46]. Very recently, proof of highly efficient photon generation via NICS in DLTs has been obtained experimentally [47], confirming the expectations and relevance of this approach.…”

“…In Figure 5, we report NICSbremsstrahlung comparisons in the case of foam thickness 25 µm and foam density 1 n c varying the parameter a 0 (20-40-50-60). We show the NICS spectra obtained with Smilei (green), the bremsstrahlung spectra from analogous simulations using the PIC code EPOCH [74] that allows for Monte Carlo evaluation of Frontiers in Physics frontiersin.org bremsstrahlung [46] (blue), and the analytical estimates of bremsstrahlung using formula 9 (red). Due to the lower efficiencies of the two processes, we consider them independent, and we do not activate NICS emission in EPOCH.…”

Laser-driven particle acceleration for multipurpose elemental analysis of materials

“…As a result, light ions (mainly protons) are accelerated from the rear surface. Exploiting the interaction with proper converters, these particles allow for generating also high-energy photons and neutrons [3,4]. Bremsstrahlung photons can be emitted following the interaction of the accelerated electrons with high-Z materials (e.g.…”