Isochoric heating and strong blast wave formation driven by fast electrons in solid-density targets

Abstract

We experimentally investigate the fast (<1 ps) isochoric heating of multi-layer metallic foils and subsequent high-pressure hydrodynamics induced by energetic electrons driven by high-intensity, high-contrast laser pulses. The early-time temperature profile inside the target is measured from the streaked optical pyrometry of the target rear side. This is further characterized from benchmarked simulations of the laser-target interaction and the fast electron transport. Despite a modest laser energy (<1 J), the early-time high pressures and associated gradients launch inwards a strong compression wave developing over 10 ps into a »140 Mbar blast wave, according to hydrodynamic simulations, consistent with our measurements. These experimental and numerical findings pave the way to a short-pulse-laser-based platform dedicated to high-energy-density physics studies.

Generation of high pressures by short-pulse low-energy laser irradiation

“…The density is reduced less rapidly out of the axis leading to the formation of a transverse blast wave travelling almost parallel to the target surface. The shock emerges out of axis also at about 4 ns, which in our case is just a fortunate coincidence, but the density is bigger, producing a clear jump in luminosity (which justifies the temporal shape of the signal recorded on the streak camera), in qualitative agreement with a previous experiment at lower laser energy [11].…”

“…As a consequence, the shock is seen to propagate in thicker targets (50 μm, instead of 20 μm as in [11]). This deeply affects the shock dynamics since the shock is now travelling in a decreasing density medium.…”

Fast collisional electron heating and relaxation in thin foils driven by a circularly polarized ultraintense short-pulse laser

“…Most laser-based isochoric heating experiments conducted so far have exploited the fast electrons driven by a linearly polarized laser pulse (Nilson et al 2010;Santos et al 2017;Sawada et al 2019). Their energy dissipation through the plasma bulk enables heating to high temperatures (0.1−1 keV) at solid-range plasma densities, but usually at the expense of poor spatial uniformity (Dervieux et al 2015) and relatively slow thermalization.…”

Enhanced relativistic-electron beam collimation using two consecutive laser pulses

“…Reducing electron beam divergence 17 as well as optimizing electron beam transport in plasmas is crucial for several important application: i) In proton acceleration induced by laser it has been proved that a transversal confinement of the electron beam increases the maximum energy of the proton beam; ii) In the fast ignition approach to ICF electron beam collimation is crucial for the success of the scheme. Previous investigations have shown that the dynamics of electron beams propagation in plasmas is mainly affected by: i) resistivity effects 13,18–25 on the electron stopping power, which become important at relativistic intensities () and reduce the final penetration length of the electron beam; ii) collisionless Weibel instabilities which start to grow and become very important for laser intensities , at the level of the plasma skin depth, generating micro magnetic fields that strongly contribute to increase the initial electron divergence 26 . Different strategies to control REB propagation in solid matter have been proposed.…”