Referierte Publikationen


D. Banaś, M. Pajek, A. Surzhykov, T. Stöhlker, C. Brandau, A. Gumberidze, C. Kozhuharov, H. F. Beyer, S. Böhm, F. Bosch, M. Czarnota, S. Chatterjee, J.-C. Dousse, S. Fritzsche, S. Hagmann, D. Liesen, P. H. Mokler, A. Müller, A. Kumar, R. Reuschl, D. Sierpowski, U. Spillmann, J. Szlachetko, S. Tashenov, S. Trotsenko, P. Verma, and A. Warczak
Subshell-selective x-ray studies of radiative recombination of U⁹²⁺ ions with electrons for very low relative energies
Phys. Rev. A, 92 :032710 (September 2015)
Radiative recombination (RR) into the K shell and L subshells of U92+ ions interacting with cooling electrons has been studied in an x-ray RR experiment at the electron cooler of the Experimental Storage Ring at GSI. The measured radiative recombination rate coefficients for electron-ion relative energies in the range 0–1000 meV demonstrate the importance of relativistic effects. The observed asymmetry of the measured K-RR x-ray emission with respect to the cooling energy, i.e., zero average relative velocity (〈vrel〉=0), are explained by fully relativistic RR calculations. With our new approach, we show that the study of the angular distribution of RR photons for different relative energies opens new perspectives for detailed understanding of the RR of ions with cooling electrons in cold magnetized plasma.
S. Luan, W. Yu, M. Y. Yu, S. Weng, J. Wang, H. Xu, H. Zhuo, and A. Y. Wong
Trapping of intense light in hollow shell
Phys. Plasmas, 22 :093110 (September 2015)
A small hollow shell for trapping laser light is proposed. Two-dimensional particle-in-cell simulation shows that under appropriate laser and plasma conditions a part of the radiation fields of an intense short laser pulse can enter the cavity of a small shell through an over-critical density plasma in an adjacent guide channel and become trapped. The trapped light evolves into a circulating radial wave pattern until its energy is dissipated.
U. Zastrau, P. Sperling, C. Fortmann-Grote, A. Becker, T. Bornath, R. Bredow, T. Döppner, T. Fennel, L. B. Fletcher, E. Förster, S. Göde, G. Gregori, M. Harmand, V. Hilbert, T. Laarmann, H. J. Lee, T. Ma, K. H. Meiwes-Broer, J. P. Mithen, C. D. Murphy, M. Nakatsutsumi, P. Neumayer, A. Przystawik, S. Skruszewicz, J. Tiggesbäumker, S. Toleikis, T. G. White, S. H. Glenzer, R. Redmer, and T. Tschentscher
Ultrafast electron kinetics in short pulse laser-driven dense hydrogen
J. Phys. B, 48 :224004 (September 2015)
Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of 10^15-10^16 W cm−2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about 25 and 40 eV for simulated delay times up to +70 fs after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and 30 eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. We resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.
M. Schnell, A. Sävert, I. Uschmann, O. Jansen, M.C. Kaluza, and C. Spielmann
Characterization and application of hard x-ray betatron radiation generated by relativistic electrons from a laser-wakefield accelerator
J. Plasma Phys., 81 :1 (August 2015)
The necessity for compact table-top x-ray sources with higher brightness, shorter wavelength and shorter pulse duration has led to the development of complementary sources based on laser-plasma accelerators, in contrast to conventional accelerators. Relativistic interaction of short-pulse lasers with underdense plasmas results in acceleration of electrons and in consequence in the emission of spatially coherent radiation, which is known in the literature as betatron radiation. In this article, we report on our recent results in the rapidly developing field of secondary x-ray radiation generated by high-energy electron pulses. The betatron radiation is characterized with a novel setup allowing to measure the energy, the spatial energy distribution in the far-field of the beam and the source size in a single laser shot. Furthermore, the polarization state is measured for each laser shot. In this way, the emitted betatron x-rays can be used as a non-invasive diagnostic tool to retrieve very subtle information of the electron dynamics within the plasma wave. Parallel to the experimental work, 3D particle-in-cell simulations were performed, proved to be in good agreement with the experimental results.
H. Bernhardt, R. Diener, P. Sungur, C. Katzer, G. Schmidl, U. Hübner, I. Uschmann, W. Fritzsche, and F. Schmidl
Engineering crystalline Au nanoparticles of anisotropic shape in epitaxially grown high-index SrTiO3
J. Mater. Sci., 50 :5562 (August 2015)
We present a possible fabrication scheme of anisotropic nanoparticles grown in a crystal high-index material (SrTiO3). Different ellipsoidal Au nano-antennas were formed by changing the Au seed layer thickness and subsequent embedding in SrTiO3, prepared by pulsed laser deposition. Prior to the SrTiO3 deposition, a temperature-induced dewetting process of the thin Au films results in different particle sizes and size distributions, which are the basis for anisotropic particle formation after embedding in a crystalline SrTiO3 matrix. The dependence of the anisotropy on the Au seed layer thickness was investigated by X-ray diffraction (XRD) measurements. At this was noticed a stronger increase in size in c-axis direction than in a/b-axis direction for an increase of the Au seed layers. Additionally, the optical response of the particles was detected via the plasmon resonance shift in extinction and scattering spectra.
M. Zürch, and C. Spielmann
Extreme ultraviolet digital in-line holography using a tabletop source
Appl. Opt., 54 :5992 (August 2015)
Digital in-line holography (DIH) offers fast, lensless, and aberration-free imaging with diffraction-limited resolution and inherently combines phase- and amplitude-contrast imaging, as well as three-dimensional imaging. Extending this technique to shorter wavelengths allows increasing the achievable spatial and phase-contrast resolution, as well as accessing material parameters not accessible in the optical domain. In this paper, we report on DIH experiments conducted with a coherent tabletop ultrafast high harmonic source operated at 38 nm wavelength. Applying a twin-image-free reconstruction scheme optimized for highly absorbing samples, we were able to demonstrate the phase-contrast imaging of silicon nitride sheets of 15 nm thickness and the use of the strong absorption of extreme ultraviolet in matter for amplitude-contrast imaging of thin films with spatial resolution below 1 μm. High-resolution morphology determination in combination with phase-contrast imaging is of special importance in thin-film characterization and applications arising thereof.
J. H. Bin, W. J. Ma, H. Y. Wang, M. J. V. Streeter, C. Kreuzer, D. Kiefer, M. Yeung, S. Cousens, P. S. Foster, B. Dromey, X. Q. Yan, R. Ramis, J. Meyer-ter-Vehn, M. Zepf, and J. Schreiber
Ion Acceleration Using Relativistic Pulse Shaping in Near-Critical-Density Plasmas
Phys. Rev. Lett., 115 :064801 (August 2015)
Ultraintense laser pulses with a few-cycle rising edge are ideally suited to accelerating ions from ultrathin foils, and achieving such pulses in practice represents a formidable challenge. We show that such pulses can be obtained using sufficiently strong and well-controlled relativistic nonlinearities in spatially well-defined near-critical-density plasmas. The resulting ultraintense pulses with an extremely steep rising edge give rise to significantly enhanced carbon ion energies consistent with a transition to radiation pressure acceleration.
P. Crump, C. Frevert, A. Ginolas, S. Knigge, A. Maabdorf, J. Lotz, W. Fassbender, J. Neukum, J. Körner, T. Topfer, A. Pranovich, M. Divoky, A. Lucianetti, T. Mocek, K. Ertel, M. De Vido, G. Erbert, and G. Trankle
Joule-Class 940-nm Diode Laser Bars for Millisecond Pulse Applications
IEEE Photon. Technol. Lett., 27 :1663 (August 2015)
The use of long resonators (for improved thermal and electrical resistance) and advanced facet passivation (for high power) is shown to enable Joule-class pulse emission from single passively cooled 1-cm diode laser bars emitting at 940 nm. Bars on CS-mount deliver pulse energy of 1 J at 60% power conversion efficiency within a 7-nm spectral window, under quasi-continuous wave conditions (1.2 ms 10 Hz). Robustness of device performance is confirmed via burn-in and multisite testing. Joule-per-bar performance is also maintained for conduction cooledmonolithic stacked arrays, adapted for bars with long resonators. Although these packages only cool the laser bar via their rear edge, peak power, lateral far field, and spectral width remain consistent with the requirements for pumping solid state lasers and scale as predicted with self-heating. An energy density >10 J/cm2 is delivered from the stack surface, for brightness >3 MW/(cm2-sr).
G. Sarri, M. E. Dieckmann, I. Kourakis, A. Di Piazza, B Reville, C. H. Keitel, and M. Zepf
Overview of laser-driven generation of electron-positron beams
J. Plasma Phys., 81 :23 (August 2015)
Electron-positron (e-p) plasmas are widely thought to be emitted, in the form of ultra-relativistic winds or collimated jets, by some of the most energetic or powerful objects in the Universe, such as black-holes, pulsars, and quasars. These phenomena represent an unmatched astrophysical laboratory to test physics at its limit and, given their immense distance from Earth (some even farther than several billion light years), they also provide a unique window on the very early stages of our Universe. However, due to such gigantic distances, their properties are only inferred from the indirect interpretation of their radiative signatures and from matching numerical models: their generation mechanism and dynamics still pose complicated enigmas to the scientific community. Small-scale reproductions in the laboratory would represent a fundamental step towards a deeper understanding of this exotic state of matter. Here we present recent experimental results concerning the laser-driven production of ultra-relativistic e-p beams. In particular, we focus on the possibility of generating beams that present charge neutrality and that allow for collective effects in their dynamics, necessary ingredients for the testing pair-plasma physics in the laboratory. A brief discussion of the analytical and numerical modelling of the dynamics of these plasmas is also presented in order to provide a summary of the novel plasma physics that can be accessed with these objects. Finally, general considerations on the scalability of laboratory plasmas up to astrophysical scenarios are given.
V. A. Zaytsev, S. Tashenov, A. V. Maiorova, V. M. Shabaev, and T. Stöhlker
Parity nonconservation effect in the resonance elastic electron scattering on heavy He-like ions
J. Phys. B, 48 :165003 (August 2015)
We investigate the parity nonconservation effect in the elastic scattering of polarized electrons on heavy He-like ions, being initially in the ground state. The enhancement of the parity violation is achieved by tuning the energy of the incident electron in resonance with quasidegenerate doubly-excited states of the corresponding Li-like ion. We consider two possible scenarios. In the first one we assume that the polarization of the scattered electron is measured, while in the second one it is not detected. For the second scenario we propose a scheme of a modified electron beam ion source (EBIS) experiment where the detection of a parity violation in the electron scattering seems possible.
C. Jauregui, H.-J. Otto, F. Stutzki, J. Limpert, and A. Tünnermann
Simplified modelling the mode instability threshold of high power fiber amplifiers in the presence of photodarkening
Opt. Express, 23 :20203 (August 2015)
In this paper we present a simple model to predict the behavior of the transversal mode instability threshold when different parameters of a fiber amplifier system are changed. The simulation model includes an estimation of the photodarkening losses which shows the strong influence that this effect has on the mode instability threshold and on its behavior. Comparison of the simulation results with experimental measurements reveal that the mode instability threshold in a fiber amplifier system is reached for a constant average heat load value in good approximation. Based on this model, the expected behavior of the mode instability threshold when changing the seed wavelength, the seed power and/or the fiber length will be presented and discussed. Additionally, guidelines for increasing the average power of fiber amplifier systems will be provided.
J. Andersson, R. Beerwerth, P. Linusson, J. H. D. Eland, V. Zhaunerchyk, S. Fritzsche, and R. Feifel
Triple ionization of atomic Cd involving 4p⁻1 and 4s⁻1 inner-shell holes
Phys. Rev. A, 92 :023414 (August 2015)
The triple ionization spectrum of atomic Cd formed upon the removal of a 4p or a 4s inner-shell electron and subsequent Auger decays has been obtained at 200 eV photon energy. By using a versatile multielectron coincidence detection technique based on a magnetic bottle spectrometer in combination with multiconfiguration Dirac-Fock calculations, Auger cascades leading to tricationic final states have been analyzed and final-state configurations have been identified. The most prominent Auger cascades leading to the ground state of Cd³⁺ have been identified in good agreement with theory.
A. M. Sayler, M. Arbeiter, S. Fasold, D. Adolph, M. Möller, D. Hoff, T. Rathje, B. Fetić, D. B. Milošević, T. Fennel, and G.G. Paulus
Accurate determination of absolute carrier-envelope phase dependence using photo-ionization
Opt. Lett., 40 :3137 (July 2015)
The carrier-envelope phase (CEP) dependence of few-cycle above-threshold ionization (ATI) of Xe is calibrated for use as a reference measurement for determining and controlling the absolute CEP in other interactions. This is achieved by referencing the CEP-dependent ATI measurements of Xe to measurements of atomic H, which are in turn referenced to ab initio calculations for atomic H. This allows for the accurate determination of the absolute CEP dependence of Xe ATI, which enables relatively easy determination of the offset between the relative CEP measured and/or controlled by typical devices and the absolute CEP in the interaction.
O. de Vries, T. Saule, M. Plötner, F. Lücking, T. Eidam, A. Hoffmann, A. Klenke, S. Hädrich, J. Limpert, S. Holzberger, T. Schreiber, R. Eberhardt, I. Pupeza, and A. Tünnermann
Acousto-optic pulse picking scheme with carrier-frequency-to-pulse-repetition-rate synchronization
Opt. Express, 23 :19586 (July 2015)
We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing.
D. Atanasov, K. Blaum, F. Bosch, C. Brandau, P. Bühler, X. Chen, I. Dillmann, T. Faestermann, B. Gao, H. Geissel, R. Gernhäuser, S. Hagmann, T. Izumikawa, P.-M. Hillenbrand, C. Kozhuharov, J. Kurcewicz, S. Litvinov, Y. Litvinov, X. Ma, G. Münzenberg, M. Najafi, F. Nolden, T. Ohtsubo, A. Ozawa, F. Ozturk, Z. Patyk, M. Reed, R. Reifarth, M. Sanjari, D. Schneider, M. Steck, T. Stöhlker, B. Sun, F. Suzaki, T. Suzuki, C. Trageser, X. Tu, T. Uesaka, P. Walker, M. Wang, H. Weick, N. Winckler, P. Woods, H. Xu, T. Yamaguchi, X. Yan, and Y. Zhang
Between atomic and nuclear physics: radioactive decays of highly-charged ions
J. Phys. B, 48 :144024 (July 2015)
Highly charged radioactive ions can be stored for extended periods of time in storage rings which allows for precision measurements of their decay modes. The straightforward motivation for performing such studies is that fully ionised nuclei or few-electron ions can be viewed as clean quantum-mechanical systems, in which the interactions of the many electrons can be either excluded or treated precisely. Thus, the influence of the electron shell on the decay probability can be investigated. Another important motivation is stellar nucleosynthesis, which proceeds at high temperatures and the involved atoms are therefore highly ionised. Presented here is a compact review of the relevant experiments conducted at heavy-ion storage rings. Furthermore, we outline the perspectives for future experiments at new-generation storage-ring facilities.
S. R. Mirfayzi, S. Kar, H. Ahmed, A. G. Krygier, A. Green, A. Alejo, R. Clarke, R. R. Freeman, J. Fuchs, D. Jung, A. Kleinschmidt, J. T. Morrison, Z. Najmudin, H. Nakamura, P. Norreys, M. Oliver, M. Roth, L. Vassura, M. Zepf, and M. Borghesi
Calibration of time of flight detectors using laser-driven neutron source
Rev. Sci. Instrum., 86 :073308 (July 2015)
Calibration of three scintillators (EJ232Q, BC422Q, and EJ410) in a time-of-flight arrangement using a laser drive-neutron source is presented. The three plastic scintillator detectors were calibrated with gamma insensitive bubble detector spectrometers, which were absolutely calibrated over a wide range of neutron energies ranging from sub-MeV to 20 MeV. A typical set of data obtained simultaneously by the detectors is shown, measuring the neutron spectrum emitted from a petawatt laser irradiated thin foil.
S. Stock, A. Surzhykov, S. Fritzsche, and D. Seipt
Compton scattering of twisted light: Angular distribution and polarization of scattered photons
Phys. Rev. A, 92 :013401 (July 2015)
Compton scattering of twisted photons is investigated within a nonrelativistic framework using first-order perturbation theory. We formulate the problem in the density-matrix theory, which enables one to gain new insights into scattering processes of twisted particles by exploiting the symmetries of the system. In particular, we analyze how the angular distribution and polarization of the scattered photons are affected by the parameters of the initial beam such as the opening angle and the projection of orbital angular momentum. We present analytical and numerical results for the angular distribution and the polarization of Compton scattered photons for initially twisted light and compare them with the standard case of plane-wave light.
A. Sävert, S. P. D. Mangles, M. Schnell, E. Siminos, J. M. Cole, M. Leier, M. Reuter, M. B. Schwab, M. Möller, K. Poder, O. Jäckel, G.G. Paulus, C. Spielmann, S. Skupin, Z. Najmudin, and M.C. Kaluza
Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy
Phys. Rev. Lett., 115 :055002 (July 2015)
We present few-femtosecond shadowgraphic snapshots taken during the nonlinear evolution of the plasma wave in a laser wakefield accelerator with transverse synchronized few-cycle probe pulses. These snapshots can be directly associated with the electron density distribution within the plasma wave and give quantitative information about its size and shape. Our results show that self-injection of electrons into the first plasma-wave period is induced by a lengthening of the first plasma period. Three-dimensional particle-in-cell simulations support our observations.
B. Ecker, B. Aurand, D. C. Hochhaus, P. Neumayer, B. Zielbauer, E. Oliva, L. Li, T. T. T. Le, Q. Jin, H. Zhao, K. Cassou, S. Daboussi, O. Guilbaud, S. Kazamias, D. Ros, P. Zeitoun, and T. Kühl
Double-stage soft x-ray laser pumped by multiple pulses applied in grazing incidence
J. Phys. B, 48 :144009 (July 2015)
In this paper we report on results obtained with a compact double-stage molybdenum x-ray laser (XRL), operated with a total pump energy of 600 mJ. The two gain regions were pumped using the double-pulse grazing incidence pumping technique, which includes travelling wave excitation for both the seed- and the amplifier-target. In addition, the influence of an additional pre-pulse has been studied. Seeded XRL operation has been demonstrated in both schemes, resulting in XRL pulses with a divergence of 2×2 mrad. The peak brilliance of the amplified XRL of 4×10²³ photons/s/mm²/mrad² in 5×10⁻⁵ relative bandwidth was more than two orders of magnitude larger compared to the original seed pulses. The presented experimental concept provides an alternative approach to the currently more common use of high-order harmonic pulses as a seed source, well suited for applications like laser spectroscopy of highly-charged ions at a storage ring.
M. Guerra, T. Stöhlker, P. Amaro, J. Machado, and J. P. Santos
Electron impact ionization cross-sections for few-electron uranium ions
J. Phys. B, 48 :144027 (July 2015)
Electron impact ionization cross sections for the U^88+ , U^89+ , U^90+ and U^91+ ions were calculated with the relativistic binary encounter Bethe model (RBEB), the modified RBEB (MRBEB) and the new MRBEB corrected by the ionic factor (MRBR–IF). Our results were compared with the available three sets of experimental data and the most used theoretical results. The MRBEB–IF results are the ones that better agree with the experimental data of the four analysed ions.
H. Stöcker, T. Stöhlker, and C. Sturm
FAIR - Cosmic Matter in the Laboratory
J. Phys.: Conf. Ser., 623 :012026 (July 2015)
To explore cosmic matter in the laboratory — this fascinating research prospect becomes available at the Facility for Antiproton and Ion Research, FAIR. The new facility is being constructed within the next five years adjacent to the existing accelerator complex of the GSI Helmholtz Centre for Heavy Ion Research at Darmstadt/Germany, expanding the research goals and technical possibilities substantially. This includes new insights into the dynamics of supernovae depending on the properties of short-lived neutron-rich nuclei which will be investigated with intense rare isotope beams. New insights will be provided into the interior of stars by exploring dense plasmas with intense heavy-ion beams combined with a high-performance laser — or into neutron star cores by probing the highest baryon densities in relativistic nucleus—nucleus collisions at unprecedented collision rates. To the latter, the properties of hadrons play an important part which will be systematically studied by high precision hadron spectroscopy with antiproton beams at unmatched intensities. The worldwide unique accelerator and experimental facilities of FAIR will open the way for a broad spectrum of unprecedented fore-front research supplying a large variety of experiments in hadron, nuclear, atomic and plasma physics as well as biomedical and material science which will be briefly described in this article. This article is based on the FAIR Green Paper and gives an update of former publications.
V. Serbo, I. P. Ivanov, S. Fritzsche, D. Seipt, and A. Surzhykov
Scattering of twisted relativistic electrons by atoms
Phys. Rev. A, 92 :012705 (July 2015)
The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams.
S. Busold, D. Schumacher, C. Brabetz, D. Jahn, F. Kroll, O. Deppert, U. Schramm, T. Cowan, A. Blazevic, V. Bagnoud, and M. Roth
Towards highest peak intensities for ultra-short MeV-range ion bunches
Sci. Rep., 5 :1 (July 2015)
A laser-driven, multi-MeV-range ion beamline has been installed at the GSI Helmholtz center for heavy ion research. The high-power laser PHELIX drives the very short (picosecond) ion acceleration on μm scale, with energies ranging up to 28.4 MeV for protons in a continuous spectrum. The necessary beam shaping behind the source is accomplished by applying magnetic ion lenses like solenoids and quadrupoles and a radiofrequency cavity. Based on the unique beam properties from the laser-driven source, high-current single bunches could be produced and characterized in a recent experiment: At a central energy of 7.8MeV, up to 5×10^8 protons could be re-focused in time to a FWHM bunch length of τ=(462±40) ps via phase focusing. The bunches show a moderate energy spread between 10% and 15% (ΔE/E0 at FWHM) and are available at 6m distance to the source und thus separated from the harsh laser-matter interaction environment. These successful experiments represent the basis for developing novel laser-driven ion beamlines and accessing highest peak intensities for ultra-short MeV-range ion bunches.
N. Frömmgen, D. L. Balabanski, M. L. Bissell, J. Bieron, K. Blaum, B. Cheal, K. Flanagan, S. Fritzsche, C. Geppert, M. Hammen, M. Kowalska, K. Kreim, A. Krieger, R. Neugart, G. Neyens, M. M. Rajabali, W. Nörtershäuser, J. Papuga, and D. T. Yordanov
Collinear laser spectroscopy of atomic cadmium: Extraction of nuclear magnetic dipole and electric quadrupole moments
Eur. Phys. J. D, 69 :164 (June 2015)
Hyperfine structure A and B factors of the atomic 5s5p ³P₂ -> 5s6s ³S₁ transition are determined from collinear laser spectroscopy data of ¹⁰⁷−¹²³Cd and ¹¹¹m−¹²³mCd. Nuclear magnetic moments and electric quadrupole moments are extracted using reference dipole moments and calculated electric field gradients, respectively. The hyperfine structure anomaly for isotopes with s₁/₂ and d₅/₂ nuclear ground states and isomeric h11/2 states is evaluated and a linear relationship is observed for all nuclear states except s₁/₂. This corresponds to the Moskowitz-Lombardi rule that was established in the mercury region of the nuclear chart but in the case of cadmium the slope is distinctively smaller than for mercury. In total four atomic and ionic levels were analyzed and all of them exhibit a similar behaviour. The electric field gradient for the atomic 5s5p ³P₂ level is derived from multi-configuration Dirac-Hartree-Fock calculations in order to evaluate the spectroscopic nuclear quadrupole moments. The results are consistent with those obtained in an ionic transition and based on a similar calculation.
G. Weber, H. Bräuning, A. Surzhykov, C. Brandau, S. Fritzsche, S. Geyer, R. E. Grisenti, S. Hagmann, C. Hahn, R. Hess, S. Hess, C. Kozhuharov, M. Kühnel, R. Märtin, N. Petridis, U. Spillmann, S. Trotsenko, D. F. A. Winters, and T. Stöhlker
Combined linear polarization and angular distribution measurements of x-rays for precise determination of multipole-mixing in characteristic transitions of high- Z systems
J. Phys. B, 48 :144031 (June 2015)
By applying novel-type position sensitive x-ray detectors as Compton polarimeters we recently performed a study of the linear polarization of Lyman-α₁ radiation following radiative electron capture into initially bare uranium ions. It was found that a model-independent determination of the ratio of the E1 and M2 transition amplitudes, and consequently of the corresponding transition rates, is feasible by combining the linear polarization data with a measurement of the angular distribution of the emitted radiation. In this work a detailed description of the underlying experimental technique for combined measurements of the linear polarization and the angular distribution of characteristic transitions in high-Z ions is presented. Special emphasis is given to the application of two, two-dimensional position-sensitive x-ray detectors for Compton polarimetry of hard x-rays. Moreover, we demonstrate the polarimeter efficiency of such detector systems can be significantly improved if events, where the charge is spread over neighboring segments, are reconstructed to be used in the polarization analysis.