Electron Vortex Generations in Photoionization of Hydrogen Atoms by Chirped-Circularly-Polarized Attosecond Pulses

By numerically solving the time-dependent Schrödinger equation and employing the analytical perturbative model, we investigate the chirp-induced electron vortex in the photoionization of hydrogen atoms by a pair of counter-rotating circularly polarized chirped attosecond XUV pulses. We demonstrate that single-photon ionization of hydrogen atoms generates photoelectron momentum distributions (PMDs) with distinct helical vortex structures either with or without a time delay between two counter-rotating circularly polarized laser pulses. These structures are highly sensitive to both the time delay between the pulses and their chirp parameters. Our analytical model reveals that the splitting of vortex spirals is caused by the sign changing of chirp-induced frequency-dependent time delay. We show that to obtain the counterpart of PMD under a pair of counter-rotating circularly polarized chirped pulses, both chirp parameters and ordering of pulses need to be reversed.