High-Energy-Density Physics and Laser Technologies

Анисимов, С. И.; Zhakhovsky, V. V.; Inogamov, N. A.; Migdal, K. P.; Petrov, Yu. V.; Хохлов, В. А.

doi:10.1134/s1063776119100169

Cited by 14 publications

(9 citation statements)

References 156 publications

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“…Similarly complex multi-step carrier thermalization sce-narios are expected also for other materials with reduced screening. The response of these systems to an optical excitation is phenomenologically often described within multi-temperature models [41] which consider the electronic system being internally thermalized for all times and therefore neglect for instance phonon emission during an internal thermalization stage [42]. The method presented here can provide valuable information on the actual state of the electron gas even on the extremely short 'non-thermal' timescales right after excitation.…”

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confidence: 99%

Ultrafast Formation of a Fermi-Dirac Distributed Electron Gas

et al. 2018

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Time-and angle-resolved photoelectron spectroscopy with 13 fs temporal resolution is used to follow the different stages in the formation of a Fermi-Dirac distributed electron gas in graphite after absorption of an intense 7 fs laser pulse. Within the first 50 fs after excitation a sequence of time frames is resolved which are characterized by different energy and momentum exchange processes among the involved photonic, electronic, and phononic degrees of freedom. The results reveal experimentally the complexity of the transition from a nascent non-thermal towards a thermal electron distribution due to the different timescales associated with the involved interaction processes. 63.20.kd, 81.05.ue, 81.05.uf The extraordinary nonlinearities and optical response times of graphitic materials suggest useful applications in photonics and electronics including light harvesting [1, 2], ultrafast photodetection [3,4], THz lasing [5,6], and saturable absorption [7,8]. Both characteristics are closely linked to the ultrafast dynamics of photoexcited carriers which for this material class is governed by weakly screened carrier-carrier scattering and carrier-phonon interaction. Fundamental aspects related to these processes were addressed in different time-domain studies in the past [9][10][11][12][13]. Because of limitations in the time resolution, most of these studies were restricted, however, to the characteristic timescales of electron-lattice equilibration, i.e., timescales ranging from ≈100 fs to ≈10 ps. The primary processes directly after photoexcitation are, in contrast, still largely unexplored and were investigated experimentally only in a few studies so far [14][15][16]. The dynamics in this strongly non-thermal regime is determined by phenomena such as transient population inversion, carrier multiplication, Auger recombination, but also phonon-mediated carrier redistribution [17][18][19][20]. The challenge is to decode the relative importance and temporal sequence of these processes that drive the electronic system from a nascent non-thermal distribution as generated by photoexcitation towards a Fermi-Dirac (FD) distribution within only ≈ 50 fs [14,15]. It is obvious that such investigations rely on experiments capable of sampling this time window at an adequate time resolution of the order of 10 fs, as well as high energy and momentum resolution. This letter reports on the non-thermal carrier dynamics in highly-oriented pyrolytic graphite (HOPG) as probed in a time-and angle-resolved photoemission spectroscopy (trARPES) experiment that is operated near the transform limit at a resolution of 13 fs (FWHM of the pumpprobe cross correlation) [21]. Over the first 100 fs, we monitor the different stages in the temporal evolution of an initially non-thermal carrier distribution generated by the absorption of a 7 fs near-infrared pulse. We are able to dissect the non-thermal to thermal transition into FIG. 1. (a) WL-pump/XUV-probe cross correlation signal of the experiment. For details see Refs. [21] and [24]. (b) ...

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Ultrafast Formation of a Fermi-Dirac Distributed Electron Gas

et al. 2018

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“…3 are Lagrangian cells in the 2T-HD calculation. The system of Lagrangian 2T hydrodynamic equations is presented in [11]. The solution of the 2T-HD equations provides the trajectory and velocity dx p (t)/dt (see Fig.…”

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confidence: 99%

“…The protective film prevents evaporation and melting. Meanwhile, the melt layer is exceptionally important for the modification of the crystal structure (see [11,Sect. 4.2]).…”

Section: Introductionmentioning

confidence: 99%

“…The elementary estimate of the pressure is p Fabs /d T , where d T is the heating depth. Heating by ultrashort laser pulses is studied in detail in [11]. The heating depth is d T = δ + d EHC , where δ is the thickness of the skin layer, which is 10-20 nm in metals irradiated by optical radiation, and d EHC is the thickness of the layer heated by a supersonic electron thermal wave, which propagates at a supersonic velocity at the two-temperature stage (2T,…”

Section: Introductionmentioning

confidence: 99%

“…(Color online) (a) Distributions of the (lines 1 and 3) electronand (lines 2 and 4) total pressures in the titanium target (lines 1 and 2) at the beginning ps and (lines 3 and 4) near the end ps of the 2T stage. Here, is the ion pressure; see, e.g.,[11]. The bulk modulus of titanium is B = 110 GPa.…”

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Melting of Titanium by a Shock Wave Generated by an Intense Femtosecond Laser Pulse

et al. 2022

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Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.

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