Laser-Induced Electron Transfer in the Dissociative Multiple Ionization of Argon Dimers

We report on an experimental and theoretical study of the ionization-fragmentation dynamics of argon dimers in intense few-cycle laser pulses with a tagged carrier-envelope phase. We find that a field-driven electron transfer process from one argon atom across the system boundary to the other argon atom triggers subcycle electron-electron interaction dynamics in the neighboring atom. This attosecond electron-transfer process between distant entities and its implications manifests itself as a distinct phase-shift between the measured asymmetry of electron emission curves of the ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{2+}$ and ${\mathrm{Ar}}^{2+}+{\mathrm{Ar}}^{2+}$ fragmentation channels. This letter discloses a strong-field route to controlling the dynamics in molecular compounds through the excitation of electronic dynamics on a distant molecule by driving intermolecular electron-transfer processes.

Figure 1

Kinetic energy release (KER) distributions of fragmentation channels $\mathrm{Ar}(n,m)$ with $(n,m)=\{(1,1),(1,2),(2,2)\}$. Arrows mark peaks due to electron recapture, shaded areas highlight the peaks resulting from Coulomb explosion at $R_{eq}$.

Figure 2

(a) Measured asymmetry ${{\mathcal{A}}_z}^{(n,m)}$ of electron emission along $z$ for $\mathrm{Ar}(n,m)$, $(n,m)=\{(1,2),(2,2)\}$ over CEP. (b) Same as (a) but simulated. The curves of the ${\mathrm{Ar}}^{+}$ monomer (gray) serve as a reference in (a) and (b). (c)–(e) Simulated distributions of ionization times of the first electron, $t_{1\mathrm{st}}$, for trajectories leading to Ar(1,2) for three values of the CEP. (f)–(h) Same as (c)–(e) but for trajectory pairs leading to Ar(2,2) with the distributions of the ionization times of the second electron, $t_{2\mathrm{nd}}$, shown in blue. The laser electric field $E_z(t)$ (gray dashed curve) is also shown for reference. The time distributions are separated depending on whether the (sum) momentum of the electron (pair) reaches positive (upper halves) or negative momentum (lower halves).

Figure 3

Classical trajectory analysis for channel Ar(2,2). (a) Ionization time distributions of first (red), $t_{1\mathrm{st}}$, and second (blue), $t_{2\mathrm{nd}}$, electrons for electron pairs emitted within [-0.25T, 0.75T] and with negative sum momentum for ${\phi }_{\mathrm{CEP}}=0$. The left (b),(d),(f) and right columns (c),(e),(g) show typical electron trajectories in space and over time, respectively. The trajectories are classified in isolated [$t_{1\mathrm{st}}\in [-0.25T,0.25T]$, (b),(c)] and concerted [$t_{1\mathrm{st}}\in [0.25T,0.75T]$, (d)–(g)]. ${\mathsf{t}}_{\mathsf{C}}$, ${\mathsf{t}}_{\mathsf{E}}$ denote the times of collision and excitation. For better visibility, the orbits in (b),(d),(f) are shown for $t>-0.1T$.

Figure 4

Simulated CEP dependence of the asymmetry ${\mathcal{A}}_z$ for channels Ar(1,2) and Ar(2,2). The latter is separated into isolated and concerted two-electron emissions based on $\mathrm{\Delta }t=t_{1\mathrm{st}}-t_{A,B,C}$, where $t_{A,B,C}$ (indicated in Fig. 2) are the instants of the laser field maxima right before a given $t_{1\mathrm{st}}$ peak that initiates the electron emission at $t_{1\mathrm{st}}$: Isolated for $0\le \mathrm{\Delta }t\le 0.25T$, concerted for $0.25T\le \mathrm{\Delta }t\le 0.5T$.