Modelling ultrafast transitions within laser-irradiated solids

Ziaja, Beata; Medvedev, Nikita

doi:10.1016/j.hedp.2011.11.004

Cited by 21 publications

(48 citation statements)

References 74 publications

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“…The Monte Carlo (MC) method is used to describe photoabsorption and Auger decays of K-shell holes, as well as the transient nonequilibrium kinetics of high-energy electrons and their secondary cascading. 11,33,35,36,38 A temperature equation is applied to describe low-energy electrons, which reach (nearly) thermal equilibrium already during the first few femtoseconds after the beginning of the laser pulse, following the "bump-on-hot-tail" distribution. 11,33,[44][45][46] The high-energy-electron and the low-energy-electron domains are interconnected, as electrons can gain or lose energy and go from one domain to another.…”

Section: Modelmentioning

confidence: 99%

“…11,33,35,36,38 A temperature equation is applied to describe low-energy electrons, which reach (nearly) thermal equilibrium already during the first few femtoseconds after the beginning of the laser pulse, following the "bump-on-hot-tail" distribution. 11,33,[44][45][46] The high-energy-electron and the low-energy-electron domains are interconnected, as electrons can gain or lose energy and go from one domain to another. This forms the source/sink terms for the temperature equation, 47,48 as the changing number and energy of low-energy electrons directly affect their temperature.…”

Section: Modelmentioning

confidence: 99%

“…11,33,[49][50][51] Incoming photons are absorbed within the simulation box, following the Lambert-Beer law, 52 with the mean attenuation length taken from Refs. 53-55.…”

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

“…This specific value of the cutoff energy has been chosen to include the exponential tail of the low-energy Fermi distribution 11,33,[44][45][46] in the "temperature" domain. In order to prove that our results are independent of a particular choice of E cut , we performed test calculations varying the value of E cut by a few eV around the cutoff value of 10 eV.…”

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

“…11,32,33 First, the photoabsorption promotes electrons from the bound states of the valence band or deep atomic shells (K shell for carbon) to the conduction band. This process occurs during the action of the laser pulse.…”

Section: Introductionmentioning

confidence: 99%

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Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

2013

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Diamond irradiated with an ultrashort intense laser pulse in the regime of photon energies from soft up to hard x rays can undergo a phase transition to graphite. This transition is induced by an excitation of electrons from the valence band or from atomic deep shells of the material into its conduction band, which is followed by a transient rapid change of the interatomic potential. Such a nonthermal phase transition occurs on a femtosecond time scale, shortly after or even during the laser pulse. In this work we show that the duration of the graphitization depends on the incoming photon energy: the higher the photon energy is, the longer the secondary electron cascading which promotes the electrons into the conduction band will take. The transient kinetics of the electronic and atomic processes during the graphitization is analyzed in detail. The damage threshold fluence is calculated in the broad photon energy range and is found to be always ∼0.7 eV/atom in terms of the average dose absorbed per atom. It is confirmed that the temporal characteristics of a femtosecond laser pulse (at a fixed pulse duration and fluence) do not significantly influence the transient damage kinetics. Finally, the influence of an additional surface layer of high-Z material on the damage within diamond is discussed.

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Section: Modelmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

“…11,33,[49][50][51] Incoming photons are absorbed within the simulation box, following the Lambert-Beer law, 52 with the mean attenuation length taken from Refs. 53-55.…”

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

2013

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Electron Kinetics in Femtosecond X‐Ray Irradiated SiO₂

Medvedev

Ziaja

Cammarata

et al. 2013

Contrib. Plasma Phys.

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A theoretical study of the ultrafast electron kinetics in solid SiO2, irradiated with a femtosecond X‐ray laser pulse, is presented. A Monte Carlo code for event‐by‐event simulations of individual particles is applied to model the electron kinetics within the irradiated SiO2 bulk. The simulation includes photoionization, elastic and inelastic scatterings of electrons, Auger decays of core holes, and electron‐hole recombination via exciton self‐trapping mechanism. Transient electron density is followed, at different photon energies and pulse durations. The change of the optical properties (reflectance, transmittance) of the material is estimated with the help of the Drude model. The analysis of the results allows us to conclude that within the X‐ray excited dielectric, the holes in the valence band give the predominant contribution to the transient changes of optical properties within the material. The increase rate of the free electron density is limited by the duration of secondary electron cascading. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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

Medvedev

Tkachenko

Ziaja

2015

Contrib. Plasma Phys.

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In this contribution we review in detail our recently developed hybrid model able to trace simultaneously nonequilibrium electron kinetics, evolution of an electronic structure, and eventually nonthermal phase transition in solids irradiated with femtosecond free-electron laser pulses. Diamond irradiated with an ultrashort intense x-ray pulse serves as an example to show how an irradiated material undergoes an ultrafast phase transition on sub-picosecond timescales. The transition of diamond into graphite is induced by an excitation of electrons from the valence band into the conduction band, which, in turn, induces a rapid change of the interatomic potential. Our theoretical model incorporates: a Monte-Carlo method for tracing high-energy electrons and K-shell holes in diamond; a temperature equation for the valence-band and low-energy conduction-band electrons; a tight binding method for calculation of the evolving electronic structure of the material and potential energy surfaces; and molecular dynamics propagating atomic trajectories. This unified approach predicts the damage threshold of diamond in a good agreement with experimentally measured values. It reveals a multi-step nature of nonthermal phase transition being an interplay between electronic excitation, changes of the band structure, and atomic reordering. An effect of pulse parameters, such as photon energy and temporal pulse shape, on the phase transition is discussed in detail.

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Modelling ultrafast transitions within laser-irradiated solids

Cited by 21 publications

References 74 publications

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

Electron Kinetics in Femtosecond X‐Ray Irradiated SiO₂

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

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Modelling ultrafast transitions within laser-irradiated solids

Cited by 21 publications

References 74 publications

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

Electron Kinetics in Femtosecond X‐Ray Irradiated SiO2

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

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Electron Kinetics in Femtosecond X‐Ray Irradiated SiO₂