Role of relativistic laser intensity on isochoric heating of metal wire targets

Abstract

In a recent experimental campaign, we used laser-accelerated relativistic hot electrons to ensure heating of thin titanium wire targets up to a warm dense matter (WDM) state [EPL 114, 45002 (2016)10.1209/0295-5075/114/45002]. The WDM temperature profiles along several hundred microns of the wire were inferred by using spatially resolved X-ray emission spectroscopy looking at the Ti Kα characteristic lines. A maximum temperature of ∼30 eV was reached. Our study extends this work by discussing the influence of the laser parameters on temperature profiles and the optimisation of WDM wire-based generation. The depth of wire heating may reach several hundreds of microns and it is proven to be strictly dependent on the laser intensity. At the same time, it is quantitatively demonstrated that the maximum WDM temperature doesn’t appear to be sensitive to the laser intensity and mainly depends on the deposited laser energy considering ranges of 6×1018–6×1020 W/cm2 and 50–200 J.

Enhancement of K-shell spectroscopy for temperature measuring of isochorically heated matter in the sub-keV range

“…The figure shows that it is not possible to describe the plasma satisfactorily under this assumption. This conclusion is consistent with some previous works, see [25,55,74].…”

“…We described the plasma by sums of spectra obtained in a stationary approximation which does not take into account the real temperature profile T(x, y, z, t), so there is no need to further discuss the physical meaning of the parameter a. All experimental spectra were processed and analysed in a similar manner as in [25,27,55]. The plasma density was assumed to be solid-state.…”

“…The HDM electron temperature profiles were determined based on the analysis of Cu K-shell line blue-shift. This is a commonly used, reliable method for temperature estimation for plasmas with an electron temperature of tens of electronvolts [25,[77][78][79], which is briefly described below.…”

“…These are exotic states of highly compressed matter with a density of the order of a solid density, 0.1-100 g cm −3 , while the temperature is 1-100 eV for WDM and >100 eV for HDM. Such studies are of interest for Another indirect heating approach that has recently been used more frequently in laser-plasma experiments is the heating of solids by laser-accelerated charged particles: electrons [25][26][27], protons and ions [28][29][30][31][32]. Such experiments have shown that it is possible to obtain a solid-state matter with temperatures up to 100s eV.…”

“…based on Ly α and He α analysis [50,54], are not applicable here. Unlike diagnostics by K-shell emission lines, which is normally used for plasma diagnostics in the range of a few tens of electronvolts [16,25,55,56]. So far, however, this method has mainly been used for the diagnosis of WDM with temperatures up to a few tens of electronvolts.…”