Carbon monoxide ionization in femtosecond bicircular laser pulses

Abstract

The CO ionization by 7.8 fs bicircular laser field consisting of the coherent superposition of two coplanar circularly polarized laser pulses is studied in the framework of the time-dependent Hartree–Fock method. Six different superpositions composed of a near-infrared pulse with wavelength of 780 nm and an ultraviolet pulse with wavelength ranging from 244 to 390 nm are considered. The intensity of the near-infrared laser pulse is 1.0 × 1014 W cm−2 and the intensity of the ultraviolet laser pulse runs from 5.0 × 1013 to 2.0 × 1014 W/cm2. Numerical results reveal that the ionization probabilities for counter-rotating field are enhanced compared to the ionization probabilities for co-rotating field only for the coherent superposition of 780 and 390 nm circularly polarized laser pulses. Our computations also emphasize that the highest occupied molecular orbital mainly contributes to CO ionization. The contribution of the inner valence molecular orbitals can be significantly increased by adjusting the intensity ratio and the relative phase between the two colors. Note that the co-rotating laser field consisting of the coherent superposition of two circularly polarized laser pulses of wavelengths 780 and 390 nm yields higher ionization probability when the positive direction of the electric field component along molecular axis points to the O nucleus.