R. Ginzel

Photoionization of N3 + and Ar8 + in an electron beam ion trap by synchrotron radiation

Photoionization (PI) of multiply and highly charged ions was studied using an electron beam ion trap and synchrotron radiation at the BESSY II electron storage ring. The versatile new method introduced here extends the range of ions accessible for PI investigations beyond current limitations by providing a dense target of ions in arbitrary, i.e. both low and high charge states. Data on near-threshold PI of N3 + and Ar8 + ions, species of astrophysical and fundamental interest, show high resolution and accuracy allowing various theoretical models to be distinguished, and highlight shortcomings of available PI calculations. We compare our experimental data with our new fully relativistic PI calculations within a multiconfiguration Dirac?Fock approach and with other advanced calculations and find generally good agreement; however, detailed examination reveals significant deviations, especially at the threshold region of Ar8 +.

X-ray laser spectroscopy of highly charged ions at FLASH

Laser spectroscopy, widely applied in physics and chemistry, is extended into the soft x-ray region for the first time. Resonant fluorescence excitation of highly charged ions (HCIs) by soft x-ray free-electron lasers (FELs) shows here the potential for unprecedented precision on photonic transitions hitherto out of reach. The novel experiments combine an electron beam ion trap (EBIT) with the Free-electron LASer at Hamburg (FLASH) to measure resonant fluorescence by trapped HCIs as a function of the lasers wavelength. The present experiments have already reached the performance of conventional soft and hard x-ray spectroscopy. We present the results obtained for three fundamental and theoretically challenging transitions in Li-like ions, namely 1s22s?2S1/2?1s22p?2P1/2 in Fe23+ at 48.6 eV, in Cu26+ at 55.2 eV and 1s22s?2S1/2?1s22p?2P3/2 in Fe23+ at 65.3 eV. The latter demonstrates laser spectroscopy of multiply or HCIs at more than one order of magnitude higher energies than hitherto reported. Resolving power leading to relative precision up to 6 parts-per-million points to the possibility of providing an atomic absolute wavelength standard in this spectral region, which is still lacking.

On the Transition Rate of the Fe x Red Coronal Line

We present a lifetime measurement of the 3s 23p 5 2 Po 1/2 first excited fine-structure level of the ground state configuration in chlorine-like Fe X, which relaxes to the ground state through a magnetic dipole (M1) transition (the so-called red coronal line) with a wavelength accurately determined to 637.454(1) nm. Moreover, the Zeeman splitting of line was observed. The lifetime of 14.2(2) ms is the most precise one measured in the red wavelength region and agrees well with advanced theoretical predictions and an empirically scaled interpolation based on experimental values from the same isoelectronic sequence.

Photoionization of ions in arbitrary charge states by synchrotron radiation in an electron beam ion trap

Photoionization of ions in various charge states is studied with an electron beam ion trap at the synchrotron BESSY II. The ion target density achieved by this method, representing an increase of up to four orders of magnitude with respect to conventional techniques, gives unprecedented access to photoionization of highly charged ions at photon energies reaching the keV range. Data on near-threshold photoionization of N3+, Ar12+, Fe12+ combined with measurements on neutral gas targets in the same setup demonstrate the versatility of this technique and show both very good resolution and accuracy.

Potential energy - induced nanostructuring of insulator surfaces by impact of slow, very highly charged ions

We have recently shown that the impact of individual slow highly charged ions is able to induce permanent nano-sized hillocks on the surface of a CaF2 single crystal. The experimentally observed threshold of the projectile ion potential energy necessary for hillock formation could be linked to a solid-liquid phase transition (nano-melting). In this contribution we report on similar nano-sized surface modifications as a result of the potential energy of impacting highly charged ions for other surfaces.

Effect of chemical etching on poly(methyl methacrylate) irradiated with slow highly charged ions

We have recently demonstrated that individual slow highly charged ions are able to produce nano-sized pits on poly(methyl methacrylate) surfaces as a result of direct ablation due to the deposition of their high potential energy, if this energy exceeds a critical minimum value. By exposing irradiated samples to a suitable etchant, such pits can be revealed even below this potential energy threshold as latent damage zones are removed. Existing pits grow both in diameter and in depth after contact with the etchant with different etching dynamics for both dimensions. Systematic studies on the response of irradiated samples to a chemical developer are presented.

Photoionizing Trapped Highly Charged Ions with Synchrotron Radiation

We review our recent high resolution experiments on photoabsorption by Fe14+ [M. C. Simon, et al., Phys. Rev. Lett. 105, 183001 (2010)], Fe15+, and Ar12+ [M. C. Simon, et al., J. Phys. B-At. Mol. Opt. Phys. 43, 065003 (2010)] at photon energies up to 1 keV. These ions play an essential role in photoionized astrophysical plasmas. Diagnostics of X-ray binary systems rely heavily on precise identification and knowledge of absorption lines. Novel experiments using an electron beam ion trap, FLASH EBIT, in combination with monochromatic synchrotron radiation allow us to investigate ions in charge states hitherto out of reach. Trapped ions can be prepared in any charge state at target densities sufficient to measure absorption cross sections below 0.1 Mb. This results in benchmark state-of-the-art predictions of the transitions wavelengths, widths, and absolute cross sections.

Nano-craters due to impact of individual highly charged ions on surfaces and thin films

We present a systematic study on nano-crater formation due to impact of individual slow highly charged ions (Xe20+ − Xe50+) on thin polymethyl-metacrylate films, which have been spin-coated on a Si-wafer.

Wechselwirkung niederenergetischer hochgeladener Ionen mit Materie

Die vorliegende Arbeit befasst sich mit experimentellen Untersuchungen der Wechselwirkung niederenergetischer hochgeladener Ionen mit neutraler Materie. Dazu wurden Messungen an Stosen langsamer Ionen mit Atomen in der Gasphase sowie mit Oberflachen durchgefuhrt. Der untersuchte Geschwindigkeitsbereich ist von grosem Interesse sowohl fur das Verstandnis von Ladungsaustauschprozessen zwischen Ionen des Sonnenwinds und astrophysikalischen Gasen, als auch fur die Erzeugung besonders oberflachennaher Nanostrukturen auf Isolatoren. Die dafur aufgebaute Anlage ermoglicht es, die kinetische Energie eines Strahls hochgeladener Ionen um mehr als zwei Grosenordnungen zu verringern und ihn auf ein gasformiges oder festes Target zu fokussieren. Durch den Einsatz einer Koinzidenzmethode zur gleichzeitigen Detektion der beim Ladungsaustausch emittierten Photonen und der dazugehorigen Projektil-Ionen konnten erstmals Reaktionskanale getrennt werden, deren Uberlagerung in fruheren Experimenten mutmaslich zu grosen Unsicherheiten und systematischen Fehlern gefuhrt haben. Dabei konnten uberraschend grose Beitrage bekannter, sowie das Auftreten bisher nur vermuteter Zerfallsprozesse im Spektrum Ladungsaustausch-induzierter Rontgenemission erstmals experimentell belegt werden.