Figure 1

(a) ${\mathrm{Ar}}^{2+}$ and ${\mathrm{Ar}}^{2+}/{\mathrm{Ar}}^{+}$ yields as a function of the XUV pump and IR probe delay. The three regions correspond to the different relative delays of the XUV and IR pulses. (b) Schematic diagram of double-ionization pathways in different regions. In region II, the main double-ionization channels are labeled as shake-off and IR-enabled Auger decay. In region I, since Auger decay is not energetically allowed, the XUV pulse creates ${\mathrm{Ar}}^{+*}$ and ${\mathrm{Ar}}^{**}$ states. These states, respectively, radiatively decay and autoionize, and do not contribute to the ${\mathrm{Ar}}^{2+}$ yield. In region III the IR pulse arrives after the XUV pulse, and doubly ionizes the ${\mathrm{Ar}}^{+*}$ and ${\mathrm{Ar}}^{**}$ states created by the XUV pulse, and opens up the LEAD channel. In region II the IR field enhances the ${\mathrm{Ar}}^{2+}$ yield by altering the atom’s electronic structure, influencing thus the LEAD, shake-up or shake-off, and other allowed channels.Reuse & Permissions

Figure 2

Calculated IR laser-enabled Auger decay rates for Ar. At lower laser intensities, the leading decay channels are the ${}^{1}S$ and ${}^{1}D(M=0)$ states. As the IR laser intensity increases, the contribution from the ${}^{1}D(M=0)$ state is larger than that from the ${}^{1}S$ state. Radiative $3p\mathrm{\text{−}}3s$ decay is represented by the dashed line.Reuse & Permissions