Ultra-intense laser interaction with nanostructured near-critical plasmas

Abstract

Near-critical plasmas irradiated at ultra-high laser intensities (I > 1018W/cm2) allow to improve the performances of laser-driven particle and radiation sources and to explore scenarios of great astrophysical interest. Near-critical plasmas with controlled properties can be obtained with nanostructured low-density materials. By means of 3D Particle-In-Cell simulations, we investigate how realistic nanostructures influence the interaction of an ultra-intense laser with a plasma having a near-critical average electron density. We find that the presence of a nanostructure strongly reduces the effect of pulse polarization and enhances the energy absorbed by the ion population, while generally leading to a significant decrease of the electron temperature with respect to a homogeneous near-critical plasma. We also observe an effect of the nanostructure morphology. These results are relevant both for a fundamental understanding and for the foreseen applications of laser-plasma interaction in the near-critical regime.

Enhanced laser-driven hadron sources with nanostructured double-layer targets

“…Laser absorption into electron kinetic energy in a near-critical plasma is a complicated, multifaceted process [52][53][54]77]. In the case of a nanostructued plasma, the absorption process is further complicated by the inhomogeneities of the density profile, which are likely to be maintained during the interaction, especially because the ion dynamics is slower than the tens-of-fs laser temporal duration [65,66]. In our scenario, the foam targets lead to an increased laser absorption into electrons.…”

“…The foam layer is generated through an extension of the diffusion-limited cluster-cluster aggregation model (DLCCA), designed to simulate the structure of fractal aggregates, such as colloids and soot [76] (a detailed description of the method is provided in [66]). The building blocks of the fractal aggregates are nanospheres having a local electron density of ∼40 n c , arranged in such a way that the filling factor is 5.7% and 3.8% for the two density values.…”

“…Indeed,the exceptional temporal contrast of modern day laser facilities [62-64] could allow a nanostructure to survive long enough to affect the interaction. In previous numerical works [65,66], we observed that a detailed modeling of the nanostructure morphology is crucial for a reliable description of the physical processes at play.In this work, by means of fully 3D particle-in-cell simulations, we model an experimental scenario of enhanced laser-driven ion acceleration where the target is a solid foil coated with a low-density nanostructured layer. A realistic morphology is used for the nanostructured layer and the laser parameters are those of a typical 30-50 Terawatt-class system.…”

“…Indeed,the exceptional temporal contrast of modern day laser facilities [62-64] could allow a nanostructure to survive long enough to affect the interaction. In previous numerical works [65,66], we observed that a detailed modeling of the nanostructure morphology is crucial for a reliable description of the physical processes at play.…”

The unexpected role of evolving longitudinal electric fields in generating energetic electrons in relativistically transparent plasmas

“…However, a characteristic enhancement in the high-energy tail of escaping electrons is a typical observation from experiments [23] and has been attributed to other acceleration mechanisms occurring in the underdense region [19,21,24]. There is significant interest in using near-critical density plasma to enhance ion acceleration mechanisms [2,5,6,8,[25][26][27][28], or to generate bright x-ray [29] or electron-positron plasmas [30] by taking advantage of the high laser energy conversion to hot electrons and the high electron temperatures.…”