Conservation laws for electron vortices in strong-field ionisation

Ultrafast Imaging of Molecular Chirality with Photoelectron Vortices

Ultrafast imaging of molecular chirality is a key step toward the dream of imaging and interpreting electronic dynamics in complex and biologically relevant molecules. Here, we propose a new ultrafast chiral phenomenon exploiting recent advances in electron optics allowing access to the orbital angular momentum of free electrons. We show that strong-field ionization of a chiral target with a few-cycle linearly polarized 800 nm laser pulse yields photoelectron vortices, whose chirality reveals that of the target, and we discuss the mechanism underlying this phenomenon. Our Letter opens new perspectives in recollision-based chiral imaging.

Carrier-envelope-phase and helicity control of electron vortices and spirals in photodetachment

Formation of electron vortices and spirals in photodetachment from the H^- anion driven by isolated ultrashort laser pulses of circular polarization or by pairs of such pulses (of either co-rotating or counter-rotating polarizations) are analyzed under the scope of the strong-field approximation. It is demonstrated that the carrier-envelope phase (CEP) and helicity of each individual pulse can be used to actively manipulate and control the vortical and spiral patterns in the probability amplitude of photodetachment. Specifically, we show that the vortical patterns can be rotated in momentum space by the CEP of the driving pulse (or, of two identical pulses); thus, offering a tool of pulse characterization. For co-rotating pulses of arbitrary CEPs, a novel type of structured vortices is discovered. Also, we demonstrate that the momentum spirals are formed when photodetachment is driven by two pulses of time-reversal symmetry, which is accompanied by absolute disappearance of vortical structures. Hence, we attribute the spiral formation to annihilation of vortices with antivortices, which are generated by time-reversed pulses comprising the train. Finally, the CEP and helicity control of spiral structures is demonstrated, leading to their rotation in momentum space.

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.

In strong field ionization, entanglement between an electron and an ion has been discussed previously. Here the authors explore orbital angular momentum entanglement between the electrons released in non-sequential double ionization.