Atomic photoionization dynamics in ultrashort cycloidal laser fields

Abstract

We present numerical simulations of ultrafast multiphoton ionization dynamics in a two-dimensional atomic model driven by co- and counterrotating circularly polarized single-color and bichromatic carrier envelope phase (CEP) stable ultrashort laser pulse sequences. Taking into account phase variations due to CEP fluctuations and the Gouy phase, our results accurately reproduce recently measured photoelectron momentum distributions [Pengel et al., Phys. Rev. Lett. 118, 053003 (2017), Phys. Rev. A 96, 043426 (2017); Kerbstadt et al., Nat. Comm. 10, 685 (2019), Adv. Phys. X 4, 1672583 (2019)]. The time evolution of the complex-valued electron wave function in coordinate and momentum space is calculated to study the bound state- and the vortex formation dynamics. The non-vanishing azimuthal probability current density proves the vortex nature of electron wave packets with odd-numbered rotational symmetry. Their angular momentum expectation value assumes half-integer values of 3.5 (corotating) and 0.5 (counterrotating). Knowledge of the wave function allows us to analyze the photoionization dynamics and to validate the physical pictures proposed in previous experimental studies. As an outlook, we investigate how electron vortices develop from the multiphoton- to the tunnel regime with increasing laser intensity.

References in corpus (8)

• Theory and applications of free-electron vortex states
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• Motion of vortex lines in quantum mechanics
• RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schrodinger equation for general, multi-electron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses
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• Modeling tomographic measurements of photoelectron vortices in counter-rotating circularly polarized laser pulses
• Generation of electron vortex states in ionization by intense and short laser pulses

Cited by in corpus (4)

• Manipulating Twisted Electrons in Strong-Field Ionization
• Exploring symmetries in photoelectron holography with two-color linearly polarized fields
• Orbital angular momentum superposition states in transmission electron microscopy and bichromatic multiphoton ionization
• Bichromatic phase-control of interfering Autler-Townes spectra