High-order harmonic generation by static coherent states method in single-electron atomic and molecular systems

We solve the time-dependent Schrodinger equation using the coherent states as basis sets for computing high harmonic generation (HHG) in a full-dimensional single-electron "realistic" system. We apply the static coherent states (SCS) method to investigate HHG in the hydrogen molecular ion induced by a linearly polarized laser field. We show that SCS gives reasonable agreement compared to the three dimensional unitary split-operator approach. Next, we study isolated attosecond pulse generation in H2+. To do so, we employ the well-known polarization gating technique, which combines two delayed counter-rotating circular laser pulses, and opens up a gate at the central portion of the superposed pulse. Our results suggest that the SCS method can be used for full-dimensional quantum simulation of higher dimensional systems such as the hydrogen molecule in the presence of an external laser field

Ultrashort laser-driven dynamics of massless Dirac electrons generating valley polarization in graphene

We identify and describe how intense short light pulses couple to massless Dirac fermions in two-dimensional systems. The ensuing excitation dynamics exhibits unusual scaling with the wavelength of the light due the linear dispersion of the band structure and the fact that light coupling is efficient only close to the Dirac points. We exploit these features to achieve valley polarization of more than 70% with simple pulse shapes. Thereby, we demonstrate that substantial valley polarization at moderate excitation can be achieved with a suitable linearly polarized pulse in gapless systems. Quantitative results are given for pristine graphene