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5Interaction of optical, soft X-ray, and hard X-ray lasers
with solids
N. Inogamov1'2
1- L.D. Landau Institute for Theoretical Physics of Russian Academy of Sciences, 142432 Chernogolovka,
prospekt Akademika Semenova, 1A, RF 2- N.L. Dukhov Automatics Research Institute (VNIIA) ROSATOM, 127055 Moscow, ulitsa Sushchevskaya, 22,
RF
This report is about the results of the recent papers [1-4]. The paper [1] is devoted to analysis of an action of ultrashort (20 fs, femtoseconds) laser pulse of hard (9 keV) X-ray on a LiF dielectric. Hard photons have a very long attenuation length datt in all materials (metals, dielectrics, semiconductors) except heavy metals with many-electron shells. This dramatically differentiates fs optical breakdown of dielectrics or fs surface ablation (metals, dielectrics) by optical lasers from the laser-matter interaction in the case with a fs hard X-ray laser with a well collimated beam (spot down to small fractions of a micron) and a huge datt. If optical breakdown is used to study polymorphic phase transitions [5-7], the mass of the region in which such a transition has taken place is limited to extremely small values from ~ 1014 to 1013 g [5,6]. In the case of the X-ray impact we are considering, this mass is three orders of magnitude larger. If we compare optical ablation and X-ray action, the mechanism of induced substance transport is fundamentally changed. In the process of optical ablation of the surface, the metal enters the vapor-plasma state and flies away (ablation - substance entrainment). Whereas in our situation, the removal into air/vacuum is small. The main displacement is cavity formation by indentation. E.g., when processing highly toxic beryllium (Be), this peculiarity is essential because only a small fraction of Be is atomized into the laboratory volume.
In [2], the propagation of a double-jump elastic - fracture laser-induced shock in diamond is considered. Understanding the behavior of matter at extreme pressures of the order of a megabar (Mbar) is essential to gain in-sight into various physical phenomena at macroscales - the formation of planets, young stars, and the cores of super-Earths, and at microscales - damage to ceramic materials and high-pressure plastic transformation and phase transitions in solids.
In [3], the melting/crystallization of titanium (Ti) by a multi-megabar shock is described. Such a shock is generated by a fs optical laser pulse (Ti:Sapp). The problem has applications in LSP (laser shock peening) - there is a refinement of large crystallites (tens of microns) to nanosize.
In [4] the coefficients of electron-phonon interaction and thermal conductivity in gold with strongly excited electron subsystem were determined.
[1] S. Makarov, et al, Damage threshold of LiF crystal irradiated by femtosecond hard XFEL pulse sequence, Opt. Express, 31, 26383-26397, (2023).
[2] S. Makarov, et al, Direct imaging of shock wave splitting in diamond at Mbar pressure, Matter and Radiation at Extremes, 8, 066601, (2023).
[3] V. Zhakhovsky, et al, Shock-induced melting and crystallization in titanium irradiated by ultrashort laser pulse, Physics of Fluids, 35(4), 096104, (2023).
[4] N. Inogamov, et al, Determination of the most important parameters of metal irradiated by ultrashort laser pulse (in Russian), Zhurnal Exp. Teor. Fiziki, 165, 165-190, (2024).
[5] S. Juodkazis, et al, Laser-Induced Microexplosion Confined in the Bulk of a Sapphire Crystal: Evidence of Multimegabar Pressures, Phys. Rev. Lett., 96, 166101, (2006).
[6] L. Smillie, et al, Exotic silicon phases synthesized through ultrashort laser-induced microexplosion: Characterization with Raman microspectroscopy, Phys. Rev. Mater., 4(9), 093803 (2020).
[7] E. Mareev, F. Potemkin, Dynamics of ultrafast phase transitions in MgF2 triggered by laser-induced THz coherent phonons, Sci. Rep., 12, 6621 (2022).
