Resonant Two-Photon Single Ionization of Two Identical Atoms

Resonant two-photon single ionization in a system consisting of two spatially well-separated identical atoms is studied. Because of two-center electron-electron correlations, the ionization may also proceed through photoexcitation of both atoms with subsequent interatomic Coulombic decay. We show that this channel may qualitatively change the dependence of the photoionization on the field intensity as well as the spectra of emitted electrons.

Figure 1

Scheme of resonant two-photon single ionization of two atoms. In order not to overload the picture, ionization channels are shown for atom $A$ only. Ionization of atom $B$ proceeds analogously.

Figure 2

Probability for single ionization of two hydrogen atoms separated by a distance $R=25\mathrm{a}.\mathrm{u}.$ given as a function of the electromagnetic pulse duration for zero detuning. The interatomic vector $\mathbf{R}$ is directed along the field polarization ${\mathbf{F}}_0$. Dot, dash, and solid curves show the results for $F_0=2\times {10}^{-6}$, $5\times {10}^{-6}$ and ${10}^{-5}\mathrm{a}.\mathrm{u}.$, respectively. (a) the contribution of the direct channel only. (b) The contribution of the two-center channel.

Figure 3

Probability for single ionization of two hydrogen atoms separated by a distance $R=25\mathrm{a}.\mathrm{u}.$ given as a function of the electromagnetic field strength for a pulse duration of 100 ps. $\mathbf{R}$ is directed along ${\mathbf{F}}_0$. Solid curve: ionization by a monochromatic field with zero detuning. Dash curve: ionization by a nonmonochromatic field with bandwidth of 20 meV and central frequency equal to the $1s\mathrm{\text{−}}2p$ transition frequency in hydrogen.

Figure 4

Energy spectrum of electrons emitted in the process of single ionization of two hydrogen atoms separated by a distance $R=25\mathrm{a}.\mathrm{u}.$ at $F_0={10}^{-4}\mathrm{a}.\mathrm{u}.$, zero detuning, pulse duration of 10 ps and $\mathbf{R}$ directed along ${\mathbf{F}}_0$. Panels (a) and (b) show the partial contributions of the direct and two-center mechanisms, respectively. Panel (c) displays the total spectrum including the interference of the two channels.