Final state selection in the $4p$ photoemission of Rb by combining laser spectroscopy with soft-x-ray photoionization

Fine structure resolved $4p$ photoemission studies have been performed on free rubidium atoms in the ground state and after excitation into the $\left[\mathrm{Kr}\right]5p{}^{2}P_{1∕2}$ and ${}^{2}P_{3∕2}$ states. The $4p^{5}5p$ final states have been excited in the $4p^{6}5s\to 4p^{5}5p$ conjugate shakeup process from ground state atoms as well as by direct photoemission from laser excited atoms. The relative intensities differ considerably in these three excitation schemes. The differences in the laser excited spectra could be described well using calculations based on the pure $jK$-coupling scheme. Thereby it was possible to specify the character of the various final states. Furthermore it has been possible to resolve two of the final states whose energy separation is smaller than the experimental resolution by selectively exciting them in a two step scheme, where the laser selects the spin-orbit coupling in the intermediate state and determines the final state coupling after x-ray photoemission.

Figure 1

Overview over the Rb $4p^{-1}$ photoemission spectrum. The spectrum covers the region of the direct photoemission and the $5s\to 5p$ conjugate shakeup. The assignment is taken from Ref. 9.

Figure 2

The $5s\to 5p$ conjugate shakeup spectrum. The assignment is taken from Ref. 9.

Figure 3

Comparison of the Rb $4p^{6}5p{}^{2}P_{J_0}\to 4p^{5}5p$ photoelectron spectra taken from the two different initial states ${}^{2}P_{3∕2}$ (upper panel) and ${}^{2}P_{1∕2}$ (lower panel). For each spectrum the dots show the measured photoelectron signal, the dashed lines give a least squares fit containing the structures from the laser-excited and unexcited atoms and the solid curve plots the electron spectrum emerging from laser excited atoms.

Figure 4

(Color online) (a) Comparison of the Rb $4p^{6}5p{}^{2}P_{J_0}\to 4p^{5}5p$ photoelectron spectra taken from the two different initial states ${}^{2}P_{3∕2}$ (black solid line) and ${}^{2}P_{1∕2}$ (cyan dashed line). The final state energy is given with respect to the ground state of neutral Rubidium atoms. (b) The theoretical spectra assuming pure $jK$-coupling as described in the text. The bars show the relative intensities of the lines (black, ${}^{2}P_{3∕2}$; cyan, ${}^{2}P_{1∕2}$) the line spectrum shows a convolution with a 56 meV Gaussian profile.