Vacuum-ultraviolet photoelectron spectroscopy of laser-excited aligned Ca atomsin the 3p-3d resonance region

In this work the autoionization of the configuration Ca 3p⁵3d4s4p of free calcium atoms has been investigated by the use of angle-resolved photoelectron spectroscopy. In a first step, atoms in the ground-state Ca 3p⁶{4s}²¹S₀ were laser excited and aligned to the first optically excited-state Ca 3p⁶{4s4p}¹P₁. From this intermediate state, with the help of synchrotron radiation (31.5--34.5 eV), the closed 3p subshell was opened, leading to the population of Ca 3p⁵3d4s4p autoionizing states. The autoionization decay of these states to both the ground state and shakeup states of singly charged ions was investigated using two types of photoelectron spectrometers. An angle-integrating spectrometer allowed us to tentatively assign the dominating angular momenta and to measure the relative partial cross sections. Furthermore, by combination with an angle-resolving spectrometer the angle dependence of the outgoing photoelectrons in the region of 32.7--33.3 eV was completely characterized for the three main diagram lines. Completeness was achieved in the sense that for action of linearly polarized light sources maximal information was extracted.