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67Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2019
ATOMISTIC MODELING OF RELAXATION IN TWO-TEMPERATURE MEDIA CREATED BY ULTRASHORT LASER PULSES
V.V. Stegailov
Joint Institute for High Temperatures of the Russian Academy of Sciences, Moscow, Russia,
e-mail: stegailov@gmail.com
Irradiation of solids with ultrashort laser pulses opened an exciting field of research. New emerging physics is connected with formation of warm dense matter (WDM) at the initial transient state of material evolution after energy deposition into electron subsystem. WDM in such ultrafast phenomena is a non-equilibrium state that makes it very challenging for theory, modelling and simulation, especially in two-temperature (2T) systems when electron and ion subsystems can be considered in quasi-equilibrium at Te>Ti. Laser ablation is one of the major phenomena where WDM properties are crucially important.
Ab initio calculations predicted the influence of electronic excitations on interatomic forces in solids [1-2]. Later this finding gained experimental support (see e.g. [3]). The development of short pulsetransient collisional soft x-ray lasers opened the possibility to study ablation of dielectric materials (for example, LiF). It was shown that the population of the conduction band in such materials leads to changes in interatomic interactions as well [4].
The model that took into account the dependence of the effective interatomic interaction in gold on Te was developed and successfully used to describe ultrafast ablation thresholds data [5,6]. Similar models can describe relaxation in heavy ions tracks [7]. However, it was found that there were significant theoretical difficulties in modeling of WDM at the ab initio level [8]. The main problem stems from the fundamental difficulty ofcalculation the full partition function for a strongly coupled electron-ion system. Among other consequences, it is manifested as a problem of proper account of total pressure in the atomistic model that required taking into account the contributions from bound electrons and from free electrons in WDM state (although such a distinction is not straightforward for the WDM regimes considered).
Considerable attention has been given to the clarification of the underlying assumptions that are implicitly used in ab initio calculations of WDM [9,10]. It was shown that the problems with describing non-equilibrium WDM states could be overcome with the use of non-abiabatic methods such as wave-packets molecular dynamics [11,12].
References
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[3] R.Ernstorfer, M.Harb, C.Hebeisen, G.Sciaini, etal. 2009 Science 323(5917) 1033-1037
[4] V.V.Stegailov Contrib. Plasma Phys. 50(1) 31-34
[5] S.V.Starikov, V.V.Stegailov, G.E.Norman, V.E.Fortov, M.Ishino, M.Tanaka, N.Hasegawa, M.Nishikino, T.Ohba, T.Kaihori, E.Ochi, T.Imazono, T.Kavachi, S.Tamotsu, T.A.Pikuz, I.Yu.Skobelev, A.Ya.Faenov 2011 JETP Lett. 93(11) 642-647
[6] G.Norman, S.Starikov, V.Stegailov, V.Fortov, I.Skobelev, T.Pikuz, A.Faenov, S.Tamotsu, Y.Kato, M.Ishino, M.Tanaka, N.Hasegawa, M.Nishikino, T.Ohba, T.Kaihori, Y.Ochi, T.Imazono, Y.Fukuda, M.Kando, T.Kawachi 2012 J. Appl. Phys. 112 013104
[7] G.E.Norman, S.V.Starikov, V.V.Stegailov, I.M.Saitov, P.A.Zhilyaev 2013 Contrib. Plasma Phys. 53(2) 128-139
[8] G.E.Norman, S.V.Starikov, V.V.Stegailov 2012 JETP 114(5) 702-800
[9] V.V.Stegailov, P.A.Zhilyaev 2015 Contrib. Plasma Phys. 55(2-3) 164-171
[10] V.V.Stegailov, P.A.Zhilyaev 2016 Molecular Physics 114(3-4) 509-518
[11] N.D.Orekhov, V.V.Stegailov 2016 J. Phys.: Conf. Ser. 774 012104
[12] N.D.Orekhov, V.V.Stegailov 2018 J. Phys.: Conf. Ser. 946 012026
