Response of GaAs to fast intense laser pulses

Abstract

Motivated by recent experiments, we have performed simulations which show in detail how the electrons and ions in GaAs respond to fast intense laser pulses ͑with durations of order 100 fs and intensities of order 1Ϫ10 TW/cm 2). The method of tight-binding electron-ion dynamics is used, in which an arbitrarily strong radiation field is included through a time-dependent Peierls substitution. The population of excited electrons, the atomic displacements, the atomic pair-correlation function, the band structure, and the imaginary part of the dielectric function are all calculated as functions of time, during and after application of each pulse. Above a threshold intensity, which results in promotion of about 10% of the electrons to the conduction band, the lattice is destabilized and the band gap collapses to zero. This is most clearly revealed in the dielectric function ⑀(), which exhibits metallic behavior and loses its structural features after 100-200 fs. ͓S0163-1829͑98͒01843-8͔

Molecular-dynamics study of ablation of solids under femtosecond laser pulses

“…Indeed, absorption of a large quantity of energy on such short timescale induces many different processes. On a microscopic scale, these include: dielectric breakdown in transparent solids, [1] change of optical and electronic properties, [2] nonthermal melting of covalent materials, [3] and semiconductorto-metal transitions. [4] On a mesoscopic scale, the pressure wave generation, [5][6][7] the thermodynamical evolution of the expanding matter, [8,9] and the identification of the collective ejection processes [8,[10][11][12][13][14][15][16][17]] must all be understood in order to provide a complete picture of the phenomenon.…”

Influence of model parameters on a simulation of x-ray irradiated materials: example of XTANT code

“…In subsection 1, we analyze the dependence on the TB parameterization, namely, the above-mentioned sp 3 basis set 24 is compared with the sp 3 s* basis set 25 . Then, in subsection 2 we proceed to the analysis of the numerical parameter γ entering Eq.…”

“…The parameters for sp 3 s* TB parameterization and corresponding repulsive term of the potential energy are taken from Ref. [25].…”

Coupling of electrons to the electromagnetic field in a localized basis

“…͑4͒, one does not need any new parameters in a calculation that employs either a semiempirical 13,14 or a first-principles-based [15][16][17][18][19] Hamiltonian H 0 whose elements are known as a function of ͑X − XЈ͒. On the other hand, this prescription is in one respect a rather crude approximation: It omits intra-atomic excitations and would therefore give no excitation at all for isolated atoms.…”

“…Here we are mainly concerned with the issue of how one can efficiently and accurately couple electrons to the electromagnetic field in such an approach, where matrix elements of various operators between localized basis functions ͑or "atomic orbitals"͒ can be calculated from first principles, and then used in large-scale calculations for complex systems, such as materials and molecules, responding to applied fields, such as ultrashort laser pulses. [9][10][11][12][13][14][15][16][17][18][19] Our starting point is, of course, the time-dependent Schrödinger equation, iប ‫ץ‬ ‫ץ‬t ͑x,t͒ = Ĥ ͑x,t͒, ͑1͒…”