Ab-initio density functional theory (DFT) has been successful for calculations of ground state properties of various materials. Time-dependent density functional theory (TDDFT) is an extension of the DFT and can describe electron dynamics in molecules, nano-structures, and solids induced by optical electric fields. We have been developing a computational method to describe electron dynamics in a crystalline solid under an irradiation of an ultrashort laser pulse, solving the time-dependent Kohn-Sham equation in real time. The method can be used for an ab-initio description of light-matter interactions. We further couple the electron dynamics calculation with the macroscopic Maxwell equations in a multiscale implementation. It can describe laser pulse propagation in dielectrics and, in particular,the energy transfer from the laser pulse to electrons in dielectrics without any empirical parameters. We apply the method to analyze recent experiments utilizing attosecond spectroscopy methods. We show a few examples. One is for the ultrafast changes of dielectric properties of diamond during the irradiation of an intense few-cycle laser pulse. We mimic the pump-probe measurement employing the multiscale Maxwell + TDDFT simulation. We clarified that the dynamical Franz-Keldysh effect is responsible for the mechanism. The other is to identify the onset of the energy transfer from the laser pulse to SiO_2 when we increase the intensity of the laser pulse. We are currently extending the analysis to obtain a clear and intuitive understanding for the initial stage of laser damage processes.
Kazuhiro Yabana, "Ab-initio calculations for energy transfer from ultrashort laser pulse to dielectrics (Conference Presentation)," Proc. SPIE 10193, Ultrafast Bandgap Photonics II, 1019304 (Presented at SPIE Defense + Security: April 10, 2017; Published: 7 June 2017); https://doi.org/10.1117/12.2263604.5459357370001.
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