Resonant coherent excitation of relativistic Ar17+ ions channeled in a Si crystal

We observed resonant coherent excitation (RCE) of Is electron to n = 2 states in Ar17+ through measurements of the survived fraction of 390 MeV/u hydrogen-like Ar17+ channeled in a Si crystal. We adopted a totally depleted Si surface barrier detector as a target crystal as well as a probe of the energy deposition. The charge state of emerged ions was measured by a combination of a charge separation magnet and a 2D-position sensitive detector. We observed the RCE for planar channeled ions by tilting the target Si crystal from the direction of [1 1 0] axis in the (2 (2) over bar 0), (0 0 4), and (I I 1) planes. Prominent resonances at tilt angles under the resonance condition were observed. Moreover, each resonance profile is split into several lines due to the I s interaction and the Stark effect originating in the static crystal field. The energy deposition in the crystal gives the information of the amplitude of the ion trajectory. The resonance peak position, intensity and width in the survived fraction of Ar17+ reflect the position dependent strength of the crystal field, the RCE and the electron loss probabilities. They are in good accord with our calculation of the transition energy and probability. (C) 1998 Elsevier Science B.V.