Nonsequential double ionization of alkaline-earth metal atoms by intense mid-infrared femtosecond pulses

Manipulating polarization effect in nonsequential double ionization

We report on a theoretical study of nonsequential double ionization (NSDI) of magnesium atoms by using combined linearly and circularly polarized fields. By employing a concise model including the dynamic ionic dipole potential, we show that the polarization effects can be controlled by tuning the subcycle waveform of the electric field of the two-color pulses. We demonstrate that the influence of the dipole potential on NSDI depends on the symmetry of two-color laser fields by tracing back the electron trajectories. Furthermore, we propose a method allowing for manipulating the returning trajectories with the initial direction of the tunneled electrons almost unchanged.

Entanglement of orbital angular momentum in non-sequential double ionization

Entanglement has a capacity to enhance imaging procedures, but this remains unexplored for attosecond imaging. Here, we elucidate that possibility, addressing orbital angular momentum (OAM) entanglement in ultrafast processes. In the correlated process non-sequential double ionization (NSDI) we demonstrate robust photoelectron entanglement. In contrast to commonly considered continuous variables, the discrete OAM allows for a simpler interpretation, computation, and measurement of entanglement. The logarithmic negativity reveals that the entanglement is robust to incoherence and an entanglement witness minimizes the number of measurements to detect the entanglement, both quantities are related to OAM coherence terms. We quantify the entanglement for a range of targets and field parameters to find the most entangled photoelectron pairs. This methodology provides a general way to use OAM to quantify and measure entanglement, well-suited to attosecond processes, and can be exploited to enhance imaging capabilities through correlated measurements, or for generation of OAM-entangled electrons.