Hydrodynamic modeling of laser interaction with micro-structured targets

Abstract

A model is developed for numerical simulations of laser absorption in plasmas made of porous materials, with particular interest in lowdensity foams. Laser absorption is treated on two spatial scales simultaneously. At the microscale, the expansion of a thin solid pore wall is modeled in one dimension and the information obtained is used in the macroscale fluid simulations for the description of the plasma homogenization behind the ionization front. This twoscale laser absorption model is implemented in the arbitrary Lagrangian-Eulerian hydrocode PALE. The numerical simulations of laser penetration into lowdensity foams compare favorably with published experimental data.

Parametric investigation of laser interaction with uniform and nanostructured near-critical plasmas

“…Moreover, ions would always retain their structure longer than electrons due to their significantly lower charge over mass ratio (at least as long as their dynamics is not relativistic). The nanostructure of low-density porous foams has been found to play a role even for intense nanosecond laser interaction with NCPs [37,38].…”

Hydrodynamics and transport processes in porous materials under terawatt laser irradiation

“…The other possible approach is to develop an "effective", or "sub-grid" model, in which the foam is approximated by an ordinary homogeneous material with the same density, but with peculiar features for what concerns the laser absorption mechanism, the thermal conduction and the response to pressure gradients [30][31][32]. This strategy allows to use existing hydrodynamic codes with few modifications and also to keep the hardware requirements and the computational cost low, really close to the ones needed for solid materials.…”

Time-dependent measurement of high-power laser light reflection by low-Z foam plasma

“…Despite many experiments performed in the last few decades and the actual experimental interest about laserfoam interaction, numerically simulating the behavior of porous materials under intense laser pulse irradiation is still a challenging task. Modeling a foam as a homogeneous material of the same average density proved to be unsuccessful when compared with the experiments [18,[25][26][27][28] . The very different spatial scales present in the problem, with thicknesses of the solid parts ranging from tens of nanometers to micrometers, and the experimental size of the typical plasma being of the order of hundreds of micrometers or millimeters, are a serious limitation for studying the foam behavior from first principles.…”

“…In fact, reproducing the internal structure of the foam material in a numerical simulation implies a high computational cost and requires the use of parallel codes and supercomputers, with quite long computational time. Recently, effective models have been developed and implemented in existing serial codes to allow reproducing the features of laser-foam interaction and energy transport in reasonable computational time [24,28,29] . In particular, the MULTI-FM code [26] is based on the use of limiters for the thermal conductivity and pressure gradient which depend on the homogenization degree of the plasma, and proved to be in very good agreement with the experimental data [24,26] .…”

“…By using the MULTI-FM code together with the experimental data, we indicate a possible strategy for estimating the homogenization time of the foam plasma, the direct measurement of which is experimentally challenging and still not achieved, despite the importance of this parameter for many applications of foams in laser-matter interaction experiments. The homogenization degree of the foam plasma determines all the peculiar features of the interaction of porous materials with laser pulses [24,26,28,29] and the measurement of the duration of the homogenization phase is particularly relevant for large-pore foams. The simulations performed with the MULTI-FM code confirm the high timeintegrated absorption efficiency of about 90% of thick layers of foam of overcritical density reported in the literature [21] .…”