Observation of inhibited electron-ion coupling in strongly heated graphite

Abstract

Creating non-equilibrium states of matter with highly unequal electron and lattice temperatures (Tele≠Tion) allows unsurpassed insight into the dynamic coupling between electrons and ions through time-resolved energy relaxation measurements. Recent studies on low-temperature laser-heated graphite suggest a complex energy exchange when compared to other materials. To avoid problems related to surface preparation, crystal quality and poor understanding of the energy deposition and transport mechanisms, we apply a different energy deposition mechanism, via laser-accelerated protons, to isochorically and non-radiatively heat macroscopic graphite samples up to temperatures close to the melting threshold. Using time-resolved x ray diffraction, we show clear evidence of a very small electron-ion energy transfer, yielding approximately three times longer relaxation times than previously reported. This is indicative of the existence of an energy transfer bottleneck in non-equilibrium warm dense matter.

High efficiency proton beam generation through target thickness control in femtosecond laser-plasma interactions

“…The results detailed here demonstrate that by scaling up the laser pulse energy to 10 J, an even greater efficiency is obtained. And while the peak proton energy is reduced in this optimised case, the energy range below 15 MeV is highly relevant for current investigations into warm dense matter 22 or biological damage studies. 23,24 In order to better understand the regime of TNSA with the laser and target parameters being considered here, the 1D radiation-hydrodynamic code HELIOS 25 was first used to model the possible disruptive effects of ASE on the thinnest target foils.…”

Single-shot measurements of plasmons in compressed diamond with an x-ray lasera)

“…13 Experiments have probed WDM heated by shocks, [14][15][16][17][18][19][20][21][22] radiation, [23][24][25] or particles 26,27 to temperatures of order 10 eV. There has been comparatively little study of matter near the transition from condensed to warm dense matter at pressures and temperatures beyond what is accessible in DACs.…”

Modeling of Nonthermal Solid‐to‐Solid Phase Transition in Diamond Irradiated with Femtosecond x‐ray FEL Pulse

“…The cascading typically occurrs on a femtosecond scale and finishes when the electron energy falls below an impact ionization threshold [32,33]. In contrast, the elastic phonon scattering can lead to a significant electron energy losses only at much longer, typically picosecond, timescales [29,34], or even longer [35].…”