Fig. 4: Effect of the spin–orbit interaction on the photoelectron quantum state in argon.
a, A schematic representation of the ionization process. Absorption of an XUV photon promotes an electron from the ground state of a neutral argon atom (3p6) to the continuum, ionizing the atom. The spin–orbit interaction splits the ionic ground state into two mutually orthogonal ionic states, 3p 52P3/2 (red) and 3p 52P1/2 (blue), separated in energy by Δϵso. Due to the conservation of energy, the resulting photoelectron spectrum is composed of two peaks, shown in red and blue, associated to the 2P3/2 and 2P1/2 states, respectively, and spaced in energy by Δϵso. The shaded area indicates the spectral region where the two peaks overlap. b, Experimentally reconstructed quantum state of a photoelectron emitted from an argon atom.
