Alignment-dependent ionization of molecules in near-circularly polarized intense laser fields

Abstract The alignment-dependent photoelectron spectrum is a valuable tool for mapping out the electronic structure of molecular orbitals. However, this approach may not be applicable to all molecules, such as CO 2 , as the ionization process in a linearly polarized laser field involves contributions from orbitals other than the highest occupied molecular orbital (HOMO). Here, we conducted a theoretical investigation into the ionization process of N 2 and CO 2 in near-circularly polarized laser field using the Coulomb-corrected strong-field approximation (CCSFA) method for molecules. In particular, we introduced a generalized dressed state into the CCSFA method in order to account for the impact of the laser field on the molecular initial state. The simulated alignment-dependent photoelectron momentum distribution (PMD) of the two molecules exhibited markedly disparate behaviors, which were in excellent agreement with the previous experimental observations reported in [ Phys. Rev. A 102 , 013117 (2020)]. Our findings indicate that under a near-circularly polarized laser field, the alignment-dependent PMD of molecules is primarily sourced from the HOMO, in contrast to the situation under a linearly polarized laser field. Moreover, a satisfactory correlation between the alignment-dependent angular distribution and the orbital symmetry was observed, which suggests an effective approach for molecular orbital imaging.