Photoelectron momentum distributions of molecules in bichromatic circularly polarized attosecond UV laser fields

Abstract

We theoretically investigate molecular photoelectron momentum distributions (MPMDs) by bichromatic [frequencies $({\ensuremath{\omega}}_{1},{\ensuremath{\omega}}_{2})]$ circularly polarized attosecond UV laser pulses. Simulations performed on aligned single-electron ${\mathrm{H}}_{2}{}^{+}$ by numerically solving the corresponding three-dimensional time-dependent Schr\odinger equation within a static nucleus frame show that MPMDs exhibit a spiral structure for both co-rotating and counter-rotating schemes. Results are analyzed by attosecond perturbation ionization models. Coherent electron wave packets created, respectively, by the two color pulses in the continuum interfere with each other. Photoionization distributions are functions of the photoelectron momentum $p$ and the ejection angle $\ensuremath{\theta}$, thus leading to spiral MPMDs. The dependence of spiral MPMDs on the time delay between the bicircular pulses and their relative phases is also presented. The spiral interference patterns are determined by the helicities and frequencies $({\ensuremath{\omega}}_{1},{\ensuremath{\omega}}_{2})$ of the bicircular fields. It is also found that the spiral patterns are sensitive to the molecular alignment and suppressed by two-center ionization interference, thus offering new tools for imaging molecular geometry.