X-ray absorption spectroscopy study of energy transport in foil targets heated by petawatt laser pulses

I Yu Skobelev ,R Kodama,P Mckenna,T A Pikuz,P Durey,D D Arich,C D Murphy,P S Bratchenko,S A Pikuz,C Spindloe,N Booth,C D Baird,S N Ryazantsev,L Doehl,D Farley,J Colgan,A Y Faenov,N C Woolsey ,Kate Lancaster ,Stephanie B Hansen

doi:10.1364/prj.6.000234

I Yu Skobelev , R Kodama + Show 18 more

Open Access

https://doi.org/10.1364/prj.6.000234

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Abstract

X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5×1020 and 2.5×1020 W/cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.

Highlights

The investigation of high-temperature plasmas at near-solid densities produced by powerful short laser pulses is pursued to increase the fundamental understanding of atomic and equations-of-state properties of material at high-energy density [1,2] and for developing several important applications, such as fast ignition of thermonuclear fusion targets [3,4,5] and the creation of bright radiographic sources [6,7]
The optical parametric chirped-pulse amplification (OPCPA) technology enables an amplified spontaneous emission (ASE)to-peak-intensity-contrast ratio below 10−9, and an additional plasma mirror was applied to improving the contrast ratio beyond 10−10 to ensure the main pulse interacting with an undisturbed cold target and achieve reproducible results
We note that the results are consistent with the conclusion in Ref. [10], where matter was heated above 500 eV at a depth of 15 μm inside a solid by a laser pulse of similar intensity and pulse duration

Summary

Introduction

The investigation of high-temperature plasmas at near-solid densities produced by powerful short laser pulses is pursued to increase the fundamental understanding of atomic and equations-of-state properties of material at high-energy density [1,2] and for developing several important applications, such as fast ignition of thermonuclear fusion targets [3,4,5] and the creation of bright radiographic sources [6,7]. Petawatt (PW) lasers with relativistic flux values efficiently generate electron beams with energies up to hundreds of megaelectronvolts (MeV) in solid-density targets. Those fast electrons penetrate the target to a depth of tens of micrometers, resulting in rapid heating of the material. The most successful methods use layered foil targets to combine materials of different atomic numbers at the front and the rear sides and analyze the selfemission from the target rear [10]. These targets are complex due to resistivity changes at the interface between material layers. While temperature gradients in the sample may be expected to complicate any quantitative analysis, we find that a simple tworegion model captures the essential features of the measured data

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Results

Conclusion