High-order harmonic generation, attosecond pulse train, and non- sequential double ionization in the helium atom under high-intensity femtosecond laser pulses

Abstract

High-order harmonic generation (HHG), attosecond pulse train (APT), and non-sequential double ionization (NSDI) in the He atom under high intense femtosecond laser pulses are calculated by time-dependent Schrodinger equation (TDSE) in one dimension (1D). By considering the mutual electron-electron and electron-nuclei interactions along with calculating the He atom ground state wave function by imaginary time propagation (ITP) method, besides calculating probability density of electrons, dipole acceleration, HHG, and APT, we could generate the well-known "knee structure" in the probability of the He atom ionization against the intensity in an ionization boundary condition model. The results are in good agreement with the experimental data reported by Walker et al. [B. Walker et al. Phys. Rev. Lett. 73, 1227 (1994)].

The modeling non-sequential double ionization of helium atom under high-intensity femtosecond laser pulses with shielding charge approximation

“…This can be interpreted more technically as follows: circularly polarized electric field prevents spreading the electron wave function in the space, more so than linearly polarized field. In an unpublished work [51], we show that the circularly polarized electric field rotates the electron wave functions around the parent ion and confine it more around the nucleus. But, the linearly polarized field moves the electrons' wave function forth and back, and causes it to spread in the space.…”