Trajectory dependent resonant coherent excitation of planar-channeled ions in a thin Si crystal

We observed resonant coherent excitation (RCE) of 1s electron to the n = 2 states in 390 MeV/u Ar17+ ions passing through thin Si crystals of about 1 μm in the {2 2 0} planar-channeling condition by measuring both the exit charge state and the exit angle of the emerged ions simultaneously in a list mode. The yield of the de-excitation X-rays from the Ar17+ ions was also measured. The thin crystal is suitable to study trajectory dependent RCE dynamics, because the exit angle of the high energy planar-channeling ion is uniquely related to the ion trajectory. From the de-excitation X-ray yield on resonance, we learned that RCE occurs with a fairly large probability within the traveling length of about 1 μm, and a majority of the excited ions survive from ionization by the collisions with target electrons or nuclei, and de-excite into the ground state by emitting the X-rays. On the other hand, the observed resonance profile of the exit charge state is shallow and broadened by the Stark effect. We found that the ionization of the excited ions takes place when the ions travel close to the atomic plane from the observed relation between the charge state and the exit angle of the emerged ions.