Laser excitation combined with $2p$ photoionization and Auger decay of potassium

The $2p$ photoionization and subsequent $L_{2,3}{M}_{2,3}{M}_{2,3}$ Auger decay spectra from free $4s_{1∕2}\to 4p_{1∕2}$ laser-excited potassium atoms are studied both experimentally and theoretically. The shake-up-structure of the $2p$ photoelectron spectrum of K is resolved. A direct experimental way for resolving the satellite structure due to conjugate shake-up transitions accompanying the hole creation in the $L_{2,3}{M}_{2,3}{M}_{2,3}$ Auger spectrum of nonexcited atoms is presented. Theoretical ab initio computations based on the multiconfiguration Dirac-Fock approach were performed to interpret the experimental findings.

Figure 1

Energy levels of $\mathrm{K}\left(4s\right)$, ${\mathrm{K}}^{*}\left(4p_{1∕2}\right)$, $\mathrm{K}\left(2p^{-1}[4s,4p,5p,5s,6s]\right)$, and $\mathrm{K}\left(3p^{-2}[4s,5s,4p]\right)$ states, computed in the single configuration approximation. All energies are taken relative to the total energy of the ground state $(-16368\mathrm{eV})$. Arrows labeled as $a–g$ denote the $2p$ photoinization from the ground state and A–E the subsequent Auger decay of $2p^{-1}5s$ state, whereas labels La–Le stand for the corresponding photoionization transitions of laser-excited K. In the rightmost diagram labels $A–H$ stand for the Auger decay of $2p^{-1}4p$ state and $A^{\prime }–E^{\prime }$ denote the Auger decay of $2p^{-1}5p$ state.

Figure 2

Experimental $LMM$ Auger spectrum of K, measured using synchrotron radiation (dashed line) and electron impact ionization (solid line).

Figure 3

(a) Experimental $2p^{-1}$ photoelectron spectrum of K; (b) experimental $2p^{-1}$ photoelectron spectrum of K, measured with $4s\to 4p_{1∕2}$ laser excitation; (c) theoretical spectra, the solid line is the $2p^{-1}$ spectrum of $\mathrm{K}\left(4s\right)$, the dotted line is the $2p^{-1}$ spectrum of ${\mathrm{K}}^{*}\left(4p_{1∕2}\right)$, and two arrows denote the energies of computed conjugate $4s\to 4p$ shake-up lines. For more details, see Fig. 1 and Table .

Figure 4

(a) Experimental potassium $LMM$ Auger spectra measured with laser on (solid line) and off (dashed line); (b) a difference spectrum taken between the laser on and off spectra shown in upper panel. The dashed line denotes the zero level. (c) The solid line represents the theoretical $2p^{-1}4p\to 3p^{-2}4p$ Auger spectrum and the dashed line the theoretical $2p^{-1}5p\to 3p^{-2}5p$ Auger spectrum.

Figure 5

(a) Experimental $LMM$ Auger electron spectrum of K; (b) theoretical spectrum including $2p^{-1}(4s,4p,5s)\to 3p^{-2}(4s,4p,5s)$ transitions; (c) theoretical $2p^{-1}4s\to 3p^{-2}4s$ spectrum (dashed line), $2p^{-1}5s\to 3p^{-2}5s$ (dotted line) and $2p^{-1}4p\to 3p^{-2}4p$ spectrum (dash dotted line).