Sequential resonant coherent excitation of Ar17+ ions in a crystal field

The resonant coherent excitation of ions in the fast oscillating electrical field, with frequencies in the x-ray range, created by the periodic Coulomb potential of a crystal target is a phenomenon which holds a large potential for spectroscopic investigations of relativistic highly charged ions. If the field frequency matches the energy difference between two electronic states, a resonant excitation of the ions becomes possible. The onset of the process can be steered by tuning the ion velocity by fix target orientation or the relative orientation of the incoming ion velocity and the crystallographic axis. If the crystal orientation simultaneously permits frequencies for two different electronic transitions, a sequential resonant excitation to higher states becomes possible. This contribution presents a series of experiments performed at the HIMAC facility with relativistic beams of H-like Ar ions and thin Silicon crystal-targets. The occurrence of the ions’ excitation was detected by measuring the charge-state distribution of the ions after the interaction with the crystal and the yield of x-rays emitted during the decay of the excited states as a function of the relative orientation of the target to the beam direction. The performed measurements clearly demonstrate that the sequential 1s -> 2p -> 3s/3d electron transition in H-like Ar was experimentally observed together with the alignment of the magnetic substates of the ions by the polarised crystal field. Experimentally obtained survival charge-state fraction of the ion yield and the x-ray emission from the excited states are in agreement with theoretical calculations based on the solution of the Schrödinger equation in the crystal potential.