High-order harmonic generation from stretched C2H2 molecules in intense laser fields

Abstract

We investigate the high harmonic generation from stretched acetylene molecules subjected to intense laser fields employing time-dependent Hartree-Fock methods. It is found that as the C-C and C-H bonds are stretched, the harmonic efficiency increases significantly due to the increased ionization of inner valence $\ensuremath{\sigma}$ orbitals in the monochromatic field, while the harmonic yield will be limited by the strong depletion of the ground-state population under a certain bond length. Moreover, the harmonic emission is affected by the nonadiabatic electron dynamics from the multiorbital coupling effects. In addition, by introducing a two-color field scheme for different C-H bond configurations with the fixed C-C bond, the aforementioned harmonic efficiency will be further enhanced due to laser-induced strong excitation from inner valence orbitals to initially unoccupied orbitals. The above results would be helpful for further understanding multiorbital dynamics in the harmonic generation from polyatomic molecules.