Laser-Induced Inelastic Diffraction from Strong-Field Double Ionization

In this Letter, we propose a novel laser-induced inelastic diffraction (LIID) scheme based on the intense-field-driven atomic nonsequential double ionization (NSDI) process and demonstrate that, with this LIID approach, the doubly differential cross sections (DDCSs) of the target ions, e.g., ${\mathrm{Ar}}^{+}$ and ${\mathrm{Xe}}^{+}$, can be accurately extracted from the two-dimensional photoelectron momentum distributions in the NSDI process of the corresponding atoms. The extracted DDCSs exhibit a strong dependence on both the target and the laser intensity, in good agreement with calculated DDCSs from the scattering of free electrons. The LIID scheme may be extended to molecular systems and provides a promising approach for imaging of the gas-phase molecular dynamics induced by a strong laser field with unprecedented spatial and temporal resolution.

Figure 1

Graphic illustration of extracting the DDCS from the momentum distribution of photoelectrons coincident with doubly charged ions. The strong-field rescattering process is depicted in the uppermost panel. In the top panel, $A$, $B$, and $C$ illustrate the key steps of the ionization process, i.e., tunneling of the valence electron ($A$), which is accelerated and returns to the core ($B$). The tunneled electron may collide inelastically with the parent ionic core to induce double ionization, whereby two electrons are freed simultaneously. The kinetic energy of one electron is close to zero while that of the other one is significantly larger. The contributions of the two orbits of the higher-energy electron will interfere with each other ($C$); see the text for details. In the middle panel, the times of the events $A$, $B$, and $C$ are marked on the temporal graph of the laser electric field. The black curve indicates the orbit with the highest return energy of 3.17 $U_p$ for the recolliding electron. The lowermost panel shows the curve (the blue-dashed semicircle) along which the DDCS is extracted; see the text for details.

Figure 2

The measured 2D photoelectron momentum distributions coincident with ${\mathrm{Xe}}^{2+}$ [(a) and (b)] and ${\mathrm{Ar}}^{2+}$ [(c) and (d)]. The laser intensities are (a) $2.0\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, (b) $3.3\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, (c) $3.6\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, and (d) $4.9\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$. The black solid circle in each panel indicates the path employed to extract the DDCS.

Figure 3

Typical DDCSs extracted from the experimental data of Fig. 2 and the calculated DDCSs of ${\mathrm{Xe}}^{+}$ [(a) and (b)] and ${\mathrm{Ar}}^{+}$ [(c) and (d)] with incident electron energies of (a) 35 eV, (b) 60 eV, (c) 70 eV, and (d) 100 eV. The experimental (theoretical) data are indicated with blue filled squares (red solid curves). The laser intensities are identical to the ones in the corresponding panels of Fig. 2.