Tunneling dynamics in multiphoton ionization and attoclock calibration

TL;DR

This paper investigates the intermediate strong-field ionization regime, developing a nonadiabatic tunneling model that reveals significant effects on electron dynamics and improves attoclock calibration accuracy.

Contribution

It introduces a nonadiabatic tunneling model incorporating Coulomb effects, enhancing understanding of electron dynamics and aiding attoclock calibration.

Findings

Nonadiabatic effects cause a transverse momentum shift and delay in electron appearance.

Coulomb interactions significantly alter tunneling exit position and electron trajectories.

Modified simpleman model improves interpretation of tunneling delay measurements.

Abstract

The intermediate domain of strong-field ionization between the tunneling and the multiphoton regimes is investigated using the strong field approximation and the imaginary-time method. An intuitive model for the dynamics is developed which describes the ionization process within a nonadiabatic tunneling picture with a coordinate dependent electron energy during the under-the-barrier motion. The nonadiabatic effects in the elliptically polarized laser field induce a transversal momentum shift of the tunneled electron wave packet at the tunnel exit, a delayed appearance in the continuum as well as a shift of the tunneling exit towards the ionic core. The latter significantly modifies the Coulomb focusing during the electron excursion in the laser field after exiting the ionization tunnel. We show that nonadiabatic effects are especially large when the Coulomb field of the ionic core is taken into account during the under-the-barrier motion. The simpleman model modified with these nonadiabatic corrections provides an intuitive background for exact theories and has direct implications for the calibration of the attoclock technique which is used for the measurement of the tunneling delay time.