Showing papers by "Joachim Schulz published in 2005"
TL;DR: The interaction of intense vacuum-ultraviolet radiation from a free-electron laser with rare gas atoms is investigated and the mechanisms of multiphoton processes were derived.
Abstract: The interaction of intense vacuum-ultraviolet radiation from a free-electron laser with rare gas atoms is investigated. The ionization products of xenon and argon atomic beams are analyzed with time-of-flight mass spectroscopy. At 98 nm wavelength and $\ensuremath{\sim}{10}^{13}\text{ }\mathrm{W}/{\mathrm{c}\mathrm{m}}^{2}$ multiple charged ions up to ${\mathrm{X}\mathrm{e}}^{6+}$ (${\mathrm{A}\mathrm{r}}^{4+}$) are detected. From the intensity dependence of multiple charged ion yields the mechanisms of multiphoton processes were derived. In the range of $\ensuremath{\sim}{10}^{12}\char21{}{10}^{13}\text{ }\mathrm{W}/{\mathrm{c}\mathrm{m}}^{2}$ the ionization is attributed to sequential multiphoton processes. The production of multiple charged ions saturates at 5\char21{}30 times lower power densities than at 193 and 564 nm wavelength, respectively.
87 citations
TL;DR: (H2O)(N) clusters generated in a supersonic expansion source with N approximately 1000 were core ionized by synchrotron radiation, giving rise to core-level photoelectron and Auger electron spectra (AES), free from charging effects.
Abstract: (H2O)N clusters generated in a supersonic expansion source with N∼1000 were core ionized by synchrotron radiation, giving rise to core-level photoelectron and Auger electron spectra (AES), free from charging effects. The AES is interpreted as being intermediate between the molecular and solid water spectra showing broadened bands as well as a significant shoulder at high kinetic energy. Qualitative considerations as well as ab initio calculations explain this shoulder to be due to delocalized final states in which the two valence holes are mostly located at different water molecules. The ab initio calculations show that valence hole configurations with both valence holes at the core-ionized water molecule are admixed to these final states and give rise to their intensity in the AES. Density-functional investigations of model systems for the doubly ionized final states—the water dimer and a 20-molecule water cluster—were performed to analyze the localization of the two valence holes in the electronic groun...
75 citations
TL;DR: The observation of relatively low-energy photoelectrons is in good agreement with calculations using a time-dependent Thomas-Fermi model and gives experimental evidence of an outer ionization process of the clusters, due to delayed thermoelectronic emission.
Abstract: The ionization dynamics of Ar and Xe clusters irradiated with intense vacuum ultraviolet light from a free-electron laser is investigated using photoelectron spectroscopy. Clusters comprising between 70 and 900 atoms were irradiated with femtosecond pulses at 95 nm wavelength (similar to 13 eV photon energy) and a peak intensity of similar to 4x10(12) W/cm(2). A broad thermal distribution of emitted electrons from clusters with a maximum kinetic energy up to 30-40 eV is observed. The observation of relatively low-energy photoelectrons is in good agreement with calculations using a time-dependent Thomas-Fermi model and gives experimental evidence of an outer ionization process of the clusters, due to delayed thermoelectronic emission.
72 citations
TL;DR: In this paper, the interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser was investigated using time-of-flight mass spectroscopy and photoelectron spectroglobalization.
Abstract: The interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser is investigated using time-of-flight mass spectroscopy and photoelectron spectroscopy. The atoms were irradiated with $100\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ pulses at $95\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ wavelength, which corresponds to $\ensuremath{\sim}13\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ photon energy. The ionization of He atoms is observed at a peak intensity of ${10}^{10}--{10}^{13}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, which is due both to nonlinear multiphoton ionization with the fundamental wavelength and single-photon ionization with third harmonic radiation of the free-electron laser. The observation of two sharp photoelectron peaks in the kinetic energy spectra, that are separated by the photon energy, is in agreement with the numerical solution of the time-dependent Schr\"odinger equation. The calculation was done using the fully quantized field and a limited but representative set of basis states. The ionization rate dependence on the laser peak intensity indicates that: (a) The low-energy peak in the photoelectron spectra is mainly due to two-photon absorption of the fundamental, but (b) the high-energy peak at $15.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ is probably due to third harmonic FEL radiation. The theoretically predicted contribution from three-photon absorption of the fundamental is of about the same order of magnitude and could not be separated from the third harmonic background signal. Particularly, the photoelectron spectra and ${\mathrm{He}}^{+}$ time-of-flight data give evidence that the intensity of third harmonic light is high enough to perform single-shot spectroscopy on gas phase samples.
21 citations
TL;DR: In this paper, the final state selection in the 4p photoemission of Rb by combining laser spectroscopy with soft x-ray photoionization was performed by combining soft X-ray photosynthesis and soft laser spectra.
Abstract: Final state selection in the 4p photoemission of Rb by combining laser spectroscopy with soft x-ray photoionization
15 citations
TL;DR: In this paper, a state-of-the-art visible laser system with the vacuum ultraviolet beamline I411 at the storage ring MAX II, shakedown satellite lines in the 2p photoelectron emission of excited Na atoms have been observed.
Abstract: In an experiment combining a state-of-the-art visible laser system with the vacuum ultraviolet beamline I411 at the storage ring MAX II, shakedown satellite lines in the 2p photoelectron emission of excited Na atoms have been observed. A close investigation of these lines shows a strong dependency of the line intensities from the linear polarization angle of the laser light. The shakedown electrons are preferably emitted into the direction of the laser electric field vector.
12 citations
01 Apr 2005-Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems
TL;DR: The MODULIGA project as discussed by the authors aims to link together the activities of the German LIGA centers Forschungszentrum Karlsruhe / Institut fur Mikro-technik, KG, Mainz (IMM) and Berliner Elektronenspeicherring-Gesellschaft fur Synchrotronstrahlung, Berlin (BESSY).
Abstract: The LIGA process combines X-ray lithography with electroplating and molding. It is a technique used worldwide for the fabrication of high aspect ratio microstructures. In Germany, this technique will be established as a production line to manufacture micro system devices. A project named (modular production method using the LIGA process) MODULIGA has the goal to link together the activities of the German LIGA centers Forschungszentrum Karlsruhe / Institut fur Mikrostrukturtechnik, Karlsruhe (FZK/IMT), Institut fur Mikrotechnik, Mainz (IMM) and Berliner Elektronenspeicherring-Gesellschaft fur Synchrotronstrahlung, Berlin (BESSY). LIGA process steps will be standardized and interface specifications will be defined to establish a modular production method. Interface specifications are defined for masks, substrate and resist, exposure technology, development and finally electroplating. The standards are defined by testing criteria. The challenges and the current status of standardization will be described.
11 citations
TL;DR: In this paper, the development of electronic states in krypton clusters was investigated by high-resolution core-level electron spectroscopy, and the energy ordering of bulk versus surface 3d(-1)np(n > 5) core-excited states in neutral clusters was demonstrated to be reversed to the 3d (-1)5p level situation.
Abstract: The development of electronic states in krypton clusters is investigated by high-resolution core-level electron spectroscopy. The energy ordering of bulk versus surface 3d(-1)np(n > 5) core-excited states in neutral clusters is demonstrated to be reversed to the 3d(-1)5p level situation. The cluster 3d(-1)6p,7p states are proven to be at a lower energy than the corresponding atomic levels. These findings reveal the ioniclike energy structure of the neutral cluster core-excited levels. The phenomenon is explained by a spatial spread of the excited orbitals over the cluster lattice.
11 citations
TL;DR: In this paper, the first experiments of rare gas cluster dynamics and spectroscopy using light from the DESY free electron laser at 13 eV were reported, showing that the energy absorption is very efficient and the clusters fragment completely.
10 citations
TL;DR: In this article, the authors question the conclusions reached by De Castro [Phys. Rev. A 72, 023409 (2005)] on photoionization of He in the presence of a strong free-electron laser radiation pulse.
Abstract: We question the conclusions reached by De Castro [Phys. Rev. A 72, 023410 (2005)] regarding the theoretical analysis of experimental results by Laarman [Phys. Rev. A 72, 023409 (2005)] on photoionization of He in the presence of a strong free-electron laser radiation pulse.