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X-rays emitted from Ar 17+ , Fe 24+ and Kr 35+ ions of about 400 MeV/u transmitting through a thin Si crystal of about 20 μm thickness have been measured in a planar channeling condition and compared with those in a random incident condition. We have found that the X-ray yield from Ar 17+ ions is larger for the channeling condition than for the random incidence, while those from Fe 24+ and Kr 35+ ions are rather smaller. Such tendencies are explained by considering the projectile dependences of excitation and ionization probabilities together with X-ray emission rates. A crude simulation has qualitatively reproduced these experimental results. When the crystal thickness is small, the X-ray yield is smaller in the channeling condition than in the random incident condition, because excitation is depressed. However, for thicker crystals, the X-ray yield is larger, since the survived population of projectile-bound electrons is larger due to small ionization probabilities under the channeling condition. This inversion occurs at a specific crystal thickness depending on projectile species. Whether the thickness of the used crystal is smaller or larger than the inversion thickness determines enhancement or depression of the X-ray yield in the channeling condition.

Resonant coherent excitation (RCE) of 390 MeV/u hydrogen-like Ar 17a ions planar channeled in a Si crystal was investigated through measurements of the de-excitation X-rays as well as the charge state distribution of the transmitted ions. We observed enhancements of both the fraction of ionized Ar 18a ions and the intensity of the de-excitation X-rays under the RCE condition. The na 2 states of Ar 17a in the crystal are split into four energy levels due to spin‐orbit interaction and Stark eAect induced by the planar potential of the crystal. The intensities of the X-rays from the lower two levels were found to be smaller compared with those from the higher two levels, which is explained by the dominance of the 2s component not decaying via a single photon emission. The diAerence between the resonance profiles of the charge state and the X-ray reflects the nature of na 2 states in the crystal field. ” 2000 Elsevier Science B.V. All rights reserved.

Resonant coherent excitation of the 1s electron to na 2 states in a hydrogen-like ion was studied through measurements of the survived fraction of 390 MeV/u Ar 17a planar channeled in a Si crystal. Adopting a totally depleted Si surface barrier detector as a target crystal, the charge state of the individual emerged ion was measured in coincidence with the energy deposition in the target. By changing the incident direction along theO2 20 U ,O 004 U, andO1 11 Uplanes, a series of clear resonances were observed as the decrease in the survived charge fraction due to higher electron loss probability for the excited state. Each resonance profile reflects energy splitting of the na 2 manifold originated from l‐ s interaction and Stark eAect due to the crystal field. From the correlation between the energy loss and survived charge fraction, transition energy as a function of the ion trajectory amplitude is deduced which is in good agreement with calculated results. ” 1998 Elsevier Science B.V. All rights reserved.

We observed resonant coherent excitation (RCE) of 1s 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 0) , (0 0 4) , and (1 1 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 l·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.

Selective production of the doubly excited state in 464 MeV/u He-like Ar${}^{16+}$ ions was accomplished using three-dimensional resonant coherent excitation in a thin foil of silicon crystal. Through a coherent interaction with the periodic crystal field, the Ar${}^{16+}$ ions were resonantly excited sequentially from the ground state to the $1s2p$ (${}^{1}\phantom{\rule{-0.16em}{0ex}}P$) state and then $2{p}^{2}$ (${}^{1}\phantom{\rule{-0.16em}{0ex}}D$) state in a way analogous to two-color x-ray laser excitation. The periodic crystal fields of 10${}^{11}$ V/m in the projectile's frame are equivalent to the fields generated by x-ray lasers with photon energies of 3139.55 and 3286.95 eV and an energy flux of 10${}^{16}$ W/cm${}^{2}$. We confirmed the doubly excited state formation through observation of the subsequent collisional ionization, Auger ionization, and radiative deexcitation.

We report on the selective production of the 2s metastable state of 390-MeV u−1 H-like Ar17+ ions by the resonant coherent excitation (RCE). The RCE to the 2s state was achieved by using Stark mixing of n = 2 states under planar channeling conditions in a 1-m thick Si crystal. The population of the 2s state was quantitatively estimated from the ionization probability in a stripper foil installed 50 mm downstream of the crystal. The 2s population was found to be 0.05 of the total number of Ar17+ ions at the stripper. The result is in good agreement with a theoretical calculation performed with the density matrix approach.

We present a joint experimental and theoretical study of convoy-electron emission resulting from highly-charged-ion transport through carbon foils at moderately relativistic speeds. Energy spectra of electrons ejected at $0\ifmmode^\circ\else\textdegree\fi{}$ have been measured for 390 MeV/u hydrogen-like ${\mathrm{Ar}}^{17+}$ ions and 460 MeV/u $(\ensuremath{\beta}=v/c=0.74,\ensuremath{\gamma}=1.49)$ ${\mathrm{Fe}}^{25+}$ $(1s),$ ${\mathrm{Fe}}^{24+}$ ${(1s}^{2}),$ and ${\mathrm{Fe}}^{23+}$ ${(1s}^{2}2s)$ incident on carbon foils with thicknesses from 25 to $8700\ensuremath{\mu}{\mathrm{g}/\mathrm{c}\mathrm{m}}^{2}.$ Due to this unprecedented wide range of thicknesses, the sequential excitation and ionization of initially deeply bound electrons to highly excited states and continuum states can be followed in considerable detail. The analysis of the spectra is aided by simulations based on the classical transport theory which has been extended to relativistic energies and to multielectron projectiles. The motion of the projectile electron inside the solid target is calculated taking into account the Coulomb potential of the projectile ion and the multiple stochastic collisions with target cores and target electrons. Different phases of the convoy-electron emissions can be disentangled: direct ejection to the continuum, the transient buildup of an excited-state wave packet followed by ionization, and postionization modification of the continuum spectrum. We find good agreement between experiment and simulation for the evolution of charge states and the emission spectrum.

An extremely-thin Germanium crystal (0.8 μm-thick) has been firstly exploited in the resonant coherent excitation (RCE) experiment. The 460 MeV/u H-like Fe25+ ions were incident on the Ge crystal under the (220) planar channeling as well as non-channeling conditions. The RCE from 1s to 2p1/2 and 2p3/2 states were successfully observed as an enhancement of the x-ray fluorescence.

We studied the anisotropy of Ly-α x-rays from H-like Ar17+ ions excited by polarization-controlled resonant coherent excitation. The effects of fine-structure depolarization on the 2p1/2 and 2p3/2 states were experimentally demonstrated as a reduction in anisotropy of decay radiation.

We demonstrate the alignment of H-like and He-like heavy ions by three-dimensional resonant coherent excitation in a thin crystalline target. The projectile ions experienced a linearly polarized oscillating field in a crystal and were excited to a specific magnetic substate, forming the aligned 2P state. We prepared the different directions of the aligned states and observed the anisotropy of deexcitation x-ray emission, which was in good agreement with theoretical estimates.

We exploited the double resonance technique in three-dimensional resonant coherent excitation to the production of hollow He-like and Li-like heavy ions. The two K-shell electron were sequentially excited to the L-shell using two frequency components of the oscillating fields arising from the different arrays of atomic planes in a Si crystal.

Convoy electrons emitted from 416 MeV/u heliumlike Ar16+ ions excited by three-dimensional resonant coherent excitation (3D-RCE) have been explored. The 1s electron in the ground state was excited to the 2p state by a periodic crystal field during the passage through a Si crystal and released into the continuum by collisions with target atoms to form a cusp-shaped peak in the energy distribution, referred to as convoy electron. Under the resonance condition, we found not only enhancement of the convoy electron yield but also significant narrowing in the energy distribution, reflecting the initial bound state momentum distribution of the excited ions. This suggests that RCE is well-suited to study fast ion collisions involving the specific excited state.

We investigated resonant coherent excitation (RCE) of 445 MeV/u Li-like Ar15+ under the planar channeling and non-channeling conditions. The K-shell and L-shell excitations are observed as decreases in the survival fraction of the Ar15+ ions after passing through a thin Si crystal. RCE under the planar channeling condition provides the opportunity to study a strong static Stark effect on the Li-like system with K-shell or L-shell vacancy. Under the non-channeling conditions, the observed excitation energies and the reported theoretical calculations were in reasonable agreement.