Multielectron ionization of three-electron strongly driven Ne at high intensities

TL;DR

This work extends the 3D ECBB semiclassical framework to high-intensity strong-field ionization of Ne, preserving the Coulomb singularity for recolliding electrons while modeling bound–bound interactions with an effective potential and smoothing transitions. It incorporates tunneling during propagation and focal-volume averaging to generate NSTI and NSDI spectra at 2–3 PW/cm$^2$, achieving good agreement with experiments for triple ionization and revealing how various ionization pathways shape the momentum spectra. The study identifies diverse pathways—direct, delayed, sequential, and cascade recollisions—whose relative importance shifts with intensity, and explains the characteristic double-peak structures and central-zero peaks in the distributions of the sum of final electron momenta. Overall, the extended ECBB framework provides a more accurate, pathway-resolved description of multi-electron ionization in strongly driven Ne and offers a route toward closer theory–experiment alignment for NSMI in multi-electron systems.

Abstract

We extend a recently developed three-dimensional semiclassical model to study double and triple ionization of Ne driven by infrared laser pulses at various intensities. This model fully accounts for the Coulomb singularity of each electron with the core, as well as for the interaction of a recolliding electron with a bound electron. The model avoids artificial autoionization by employing effective Coulomb potentials to describe the interaction between bound electrons. Using the extended effective-Coulomb-potential for bound-bound electrons (ECBB) model, we compute triple and double ionization spectra. For instance, we compute the distributions of the sum of the final momenta along the laser field of the escaping electrons. Taking focal volume averaging into account, we find very good agreement with experimental results, particularly for triple ionization. Also, we identify the main pathways of triple and double ionization and explain how these pathways give rise to the main features of the triple and double ionization spectra.

Figures (8)

• Figure 1: For Ne, we plot the ratio of double to triple ionization probability obtained with the extended ECBB model (black circles), with the ECBB model when tunneling is not accounted for (light gray diamonds) and compare with experiment (gray squares) Rudenko_2008. These results are obtained without focal volume averaging.
• Figure 2: For double ionization, we plot the probability distributions of the sum of the final electron momenta along the laser field at intensities 2 PW/cm$^2$ (a) and 3 PW/cm$^2$ (b), accounting for focal volume averaging. Results are obtained with the ECBB model (black solid lines) and experimentally Zrost_2006PhysRevLett.93.253001 (purple solid lines). Also, at each intensity, we separate the double ionization events depending on whether an electron does or does not tunnel at least once during time propagation. We plot the respective distributions for double ionization events with tunneling (light gray dotted lines) and without tunneling (dark gray dashed-dotted lines). The experimental and total theoretical distributions are normalized to one, while the distributions with and without tunneling events are normalized to their respective contribution to double ionization.
• Figure 3: For triple ionization, we plot probability distributions as in Fig. \ref{['fig:SOM_DI_FVA']} and compare with experimental results Rudenko_2008.
• Figure 4: Percentage contribution of the main pathways of triple ionization as a function of intensity.
• Figure 5: Examples of trajectories in triple ionization pathways for Ne driven by a 25 fs, 800nm laser at 3 PW/cm$^2$. We plot the position of each of the three electrons along the field, electron 1 (red line), electron 2 (blue line) and electron 3 (gray line), while the electric field is depicted with a green dotted line. Each black arrow depicts the time of recollision between a quasifree electron and one or more bound electrons. A gray arrow indicates the time when an electron tunnels during time propagation. The pathways shown are direct (e$^-$, 3e$^-$) (a), delayed (e$^-$, 2e$^-$) (b), delayed (e$^-$, e$^-$) (c), sequential (d), e$^{-}$ + DI of Ne$^{+}$ (e), cascade of recollisions (f).