Multiphoton inner-shell ionization of the carbon atom

We apply time-dependent $R$-matrix theory to study inner-shell ionization of C atoms in ultrashort high-frequency light fields with a photon energy between 170 and 245 eV. At an intensity of ${10}^{17}$ $W/{\mathrm{cm}}^2$, ionization is dominated by single-photon emission of a $2\ell$ electron, with two-photon emission of a $1s$ electron accounting for about 2–3% of all emission processes, and two-photon emission of $2\ell$ contributing about 0.5–1%. Three-photon emission of a $1s$ electron is estimated to contribute about 0.01–0.03%. Around a photon energy of 225 eV, two-photon emission of a $1s$ electron, leaving ${\mathrm{C}}^{+}$ in either $1s2s2p^3$ or $1s2p^4$, is resonantly enhanced by intermediate $1s2s^{2}2p^3$ states. The results demonstrate the capability of time-dependent $R$-matrix theory to describe inner-shell ionization processes including rearrangement of the outer electrons.

Figure 1

Yields for one- and two-photon emission of a $2\ell$ electron and two- and three-photon emission of a $1s$ electron from neutral C irradiated by a short laser pulse with a peak intensity of ${10}^{17}$ W/${\mathrm{cm}}^2$ as a function of photon energy. The three-photon emission yield is estimated through subtraction of the single-photon yield induced by the edges of the pulse bandwidth. Data associated with this report can be accessed via [30].

Figure 2

Photoionization yields for residual-ion configurations of ${\mathrm{C}}^{+}$ as a function of photon energy at an intensity of ${10}^{17}$ W/${\mathrm{cm}}^2$.