Investigation of vortex arms in electron vortices by counter-rotating elliptically polarized attosecond laser pulses

We theoretically investigate the vortex patterns in photoelectron momentum distributions of He⁺ driven by counter-rotating elliptically polarized, time delayed attosecond laser pulses by numerically solving the two-dimensional time-dependent Schrödinger equation. It is found that the number of vortex arms is extremely sensitive to the ellipticity and wavelength of counter-rotating elliptically polarized laser pulses, which is illustrated by the attosecond perturbation ionization models. In addition, the effect of different time delays between two pulses on the interference patterns is also investigated and the corresponding physical mechanism is demonstrated. Since the wavelength, ellipticity and time delay have a significant effect on the vortex interference patterns, this may be a new method for laser field detection.