Real time-TDDFT study of thermal and non-thermal lattice dynamics depending on laser pulse-width

In this work, I will discuss lattice dynamics of α-quartz conducted by femtosecond laser by performing the real-time TDDFT Ehrenfest dynamics with use of plane-wave basis set, TM type pseudopotentials, and adiabatic LDA functional. The α-quartz was expressed by a slab model with hydrogen termination. The distribution of kinetic energy for silicon and oxygen atoms was found to be nearly equal under shinning the femtosecond laser with full-width of half-maximum (FWHM) 100 fs, wave length 800 nm, and fluence 10 J/cm². It is therefore concluded that this pulse width gave thermal dynamics on the lattice. By fixing the wave length and fluence of the femtosecond laser, the lattice dynamics with shorter FWHM was examined and non-equal distribution of kinetic energies among silicon and oxygen atoms was found. Furthermore, shorter pulse with FWHM=10 fs conducted ablation. I will discuss the physics behind this phenomenon.