Comparative Study of Electron Vortices in Photoionization of Molecules and Atoms by Counter-Rotating Circularly Polarized Laser Pulses

We comparatively study the effect of orbital symmetry on vortex patterns in photoelectron momentum distributions (PMDs) of perfectly aligned H2 and N2 molecules and their companion atom Ar exposed to a pair of delayed counter-rotating circularly polarized lasers by numerically solving the two-dimensional time-dependent Schrödinger equation. We show that vortex patterns in PMDs strongly depend on the orbital symmetry of atoms and molecules, and numbers of spiral arms in PMDs of N2, H2, and Ar are quite different even though they have nearly identical ionization potentials. We also confirm that vortex structures in PMDs of the highest occupied molecular orbit (HOMO)-2 for N2 are quite different from those of the HOMO but similar to those of Ar. Furthermore, vortex patterns in PMDs of molecules are also sensitive to internuclear distances and alignment angles, which provides more possibilities for controlling the coherent interference of electronic wave packets in comparison with atoms.