Multiphoton Double Ionization of Ar and Ne Close to Threshold

In kinematically complete studies we explore double ionization (DI) of Ne and Ar in the threshold regime ($I>3\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$) for 800 nm, 45 fs pulses. The basic differences are found in the two-electron momentum distributions—“correlation” (CO) for Ne and “anticorrelation” (ACO) for Ar—that can be partially explained theoretically within a 3D classical model including tunneling. Transverse electron momentum spectra provide insight into “Coulomb focusing” and point to correlated nonclassical dynamics. Finally, DI threshold intensities, CO as well as ACO regimes are predicted for both targets.

Figure 1

Parallel momentum correlation of two electrons for argon (a) ($3\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$) and neon (c) ($1.5\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$). (b) Transverse momentum distributions of electrons in coincidence with ${\mathrm{Ar}}^{1+}$ (dotted line) and ${\mathrm{Ar}}^{2+}$ at $3\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$ (solid line) and at $7\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$ (dashed solid line) as well as (d) for ${\mathrm{Ne}}^{1+}$ and ${\mathrm{Ne}}^{2+}$ at $1.5\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$.

Figure 2

Same as Fig. 1 but for theoretical calculations (see text).

Figure 3

Predicted areas where correlated or anticorrelated electron emission dominates as well as the boundary below which DI should be forbidden at all. Points indicate the present measurement where correlation (circle), anticorrelation (square), and no DI (triangle) have been observed, respectively.