Abstract
Abstract Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion. Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task. In this work, we report, for the first time to the best of our knowledge, the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density. The experiments have been performed with the ABC laser, with targets constituted by foam of overcritical density and by solid media of the same chemical composition. We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results. Using the simulations together with the experimental results, we indicate a criterion for estimating the homogenization time of the laser-produced plasma, whose measurement is challenging with direct diagnostic techniques and still not achieved.
Highlights
Porous materials, or foams, have a non-trivial internal structure, constituted by randomly arranged solid parts, which can be filaments or membranes, separated by empty spaces[1]
In this work we have presented, for the first time, the timeresolved measurement of the reflected light of a terawatt Ndlaser pulse from a target made from a foam of overcritical density with large pores, obtained in experiments performed at the ABC facility
We have found that the internal structure of the foam manifests itself by inducing oscillations of the reflected light signals
Summary
Foams, have a non-trivial internal structure, constituted by randomly arranged solid parts, which can be filaments or membranes, separated by empty spaces[1]. Radiation absorption occurs volumetrically at the homogenization depth in the case of a foam with an average density lower than the critical plasma density (subcritical foam), and in one with a supercritical average density (overcritical foam)[20] This is the reason for the higher absorption efficiency of laser radiation in the plasma of a porous substance compared with the plasma of a solid target. 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 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]
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