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Publikationen von
Dr. Sonja Bernitt

Alle Publikationen des HI Jena


J. Stierhof, S. Kühn, M. Winter, P. Micke, R. Steinbrügge, C. Shah, N. Hell, M. Bissinger, M. Hirsch, R. Ballhausen, M. Lang, C. Gräfe, S. Wipf, R. Cumbee, G. L. Betancourt-Martinez, S. Park, J. Niskanen, M. Chung, F. S. Porter, T. Stöhlker, T. Pfeifer, G. V. Brown, S. Bernitt, P. Hansmann, J. Wilms, J. R. Crespo López-Urrutia, and M. A. Leutenegger
A new benchmark of soft X-ray transition energies of Ne, CO2, and SF6: paving a pathway towards ppm accuracy
The European Physical Journal D 76, 38 (2022)

Abstract: A key requirement for the correct interpretation of high-resolution X-ray spectra is that transition energies are known with high accuracy and precision. We investigate the K-shell features of Ne, CO2, and SF6 gases, by measuring their photo ion-yield spectra at the BESSY II synchrotron facility simultaneously with the 1s–np fluorescence emission of He-like ions produced in the Polar-X EBIT. Accurate ab initio calculations of transitions in these ions provide the basis of the calibration. While the CO2 result agrees well with previous measurements, the SF6 spectrum appears shifted by ∼0.5 eV, about twice the uncertainty of the earlier results. Our result for Ne shows a large departure from earlier results, but may suffer from larger systematic effects than our other measurements. The molecular spectra agree well with our results of time-dependent density functional theory. We find that the statistical uncertainty allows calibrations in the desired range of 1–10 meV, however, systematic contributions still limit the uncertainty to ∼40–100 meV, mainly due to the temporal stability of the monochromator energy scale. Combining our absolute calibration technique with a relative energy calibration technique such as photoelectron energy spectroscopy will be necessary to realize its full potential of achieving uncertainties as low as 1–10 meV.


M. A. Leutenegger, S. Kühn, P. Micke, R. Steinbrügge, J. Stierhof, C. Shah, N. Hell, M. Bissinger, M. Hirsch, R. Ballhausen, M. Lang, C. Gräfe, S. Wipf, R. Cumbee, G. L. Betancourt-Martinez, S. Park, V. A. Yerokhin, A. Surzhykov, W. C. Stolte, J. Niskanen, M. Chung, F. S. Porter, T. Stöhlker, T. Pfeifer, J. Wilms, G. V. Brown, J. R. C. López-Urrutia, and S. Bernitt
High-Precision Determination of Oxygen Kα Transition Energy Excludes Incongruent Motion of Interstellar Oxygen
Physical Review Letters 125, 243001 (2020)

Abstract: We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O2 with 8 meV uncertainty. We reveal a systematic ∼450  meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O2 literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.

M. Togawa, S. Kühn, C. Shah, P. Amaro, R. Steinbrügge, J. Stierhof, N. Hell, M. Rosner, K. Fujii, M. Bissinger, R. Ballhausen, M. Hoesch, J. Seltmann, S. Park, F. Grilo, F. S. Porter, J. P. Santos, M. Chung, T. Stöhlker, J. Wilms, T. Pfeifer, G. V. Brown, M. A. Leutenegger, S. Bernitt, and J. R. C. López-Urrutia
Observation of strong two-electron–one-photon transitions in few-electron ions
Physical Review A 102, 052831 (2020)

Abstract: We resonantly excite the K series of O5+ and O6+ up to principal quantum number n=11 with monochromatic x rays, producing K-shell holes, and observe their relaxation by soft-x-ray emission. Some photoabsorption resonances of O5+ reveal strong two-electron–one-photon (TEOP) transitions. We find that for the [(1s2s)15p3/2]3/2;1/2 states, TEOP relaxation is by far stronger than the radiative decay and competes with the usually much faster Auger decay path. This enhanced TEOP decay arises from a strong correlation with the near-degenerate upper states [(1s2p3/2)14s]3/2;1/2 of a Li-like satellite blend of the He-like Kα transition. Even in three-electron systems, TEOP transitions can play a dominant role, and the present results should guide further research on the ubiquitous and abundant many-electron ions where electronic energy degeneracies are far more common and configuration mixing is stronger.

S. Kühn, C. Shah, J. López-Urrutia, K. Fujii, R. Steinbrügge, J. Stierhof, M. Togawa, Z. Harman, N. Oreshkina, C. Cheung, M. Kozlov, S. Porsev, M. Safronova, J. Berengut, M. Rosner, M. Bissinger, R. Ballhausen, N. Hell, S. Park, M. Chung, M. Hoesch, J. Seltmann, A. Surzhykov, V. Yerokhin, J. Wilms, F. Porter, T. Stöhlker, C. Keitel, T. Pfeifer, G. Brown, M. Leutenegger, and S. Bernitt
High Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength Problem
Physical Review Letters 124, 225001 (2020)

Abstract: For more than 40 years, most astrophysical observations and laboratory studies of two key soft x-ray diagnostic 2p-3d transitions, 3C and 3D, in Fe XVII ions found oscillator strength ratios f(3C)/f(3D) disagreeing with theory, but uncertainties had precluded definitive statements on this much studied conundrum. Here, we resonantly excite these lines using synchrotron radiation at PETRA III, and reach, at a millionfold lower photon intensities, a 10 times higher spectral resolution, and 3 times smaller uncertainty than earlier work. Our final result of f(3C)/f(3D)=3.09(8)(6) supports many of the earlier clean astrophysical and laboratory observations, while departing by five sigmas from our own newest large-scale ab initio calculations, and excluding all proposed explanations, including those invoking nonlinear effects and population transfers.


L. Mercadier, A. Benediktovitch, C. Weninger, M. Blessenohl, S. Bernitt, H. Bekker, S. Dobrodey, A. Sanchez-Gonzalez, B. Erk, C. Bomme, R. Boll, Z. Yin, V. Majety, R. Steinbrügge, M. Khalal, F. Penent, J. Palaudoux, P. Lablanquie, A. Rudenko, D. Rolles, J. C. López-Urrutia, and N. Rohringer
Evidence of Extreme Ultraviolet Superfluorescence in Xenon
Physical Review Letters 123, 023201 (2019)

Abstract: We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a free-electron laser pulse in a cell filled with Xe gas, the medium is quasi-instantaneously population inverted by 4d-shell ionization on the giant resonance followed by Auger decay. On the timescale of ∼10 ps to ∼100 ps (depending on parameters) a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe lines in the forward direction. As the number of emitters in the system is increased by either raising the pressure or the pump-pulse energy, the emission yield grows exponentially over four orders of magnitude and reaches saturation. With increasing yield, we observe line broadening, a manifestation of superfluorescence in the spectral domain. Our novel theoretical approach, based on a full quantum treatment of the atomic system and the irradiated field, shows quantitative agreement with the experiment and supports our interpretation.

G. Betancourt-Martinez, H. Akamatsu, D. Barret, M. Bautista, S. Bernitt, S. Bianchi, D. Bodewits, N. Brickhouse, G. V. Brown, E. Costantini, M. Coreno, J. R. C. López-Urrutia, R. Cumbee, M. Eckart, G. Ferland, F. Fiore, M. Fogle, A. Foster, J. Garcia, T. Gorczyca, V. Grinberg, N. Grosso, L. Gu, M. F. Gu, M. Guainazzi, N. Hell, J.-W. d. Herder, J. Kaastra, T. Kallman, J. Lee, M. Leutenegger, J. Marler, D. McCammon, S. Nakashima, F. Nicastro, F. Paerels, F. Pajot, E. Pointecouteau, D. Porquet, F. S. Porter, D. W. Savin, M. Sawada, C. Shah, A. Simionescu, M. d. Simone, C. Sosolik, P. Stancil, R. Steinbrügge, and H. Yamaguchi
Unlocking the Capabilities of Future High-Resolution X-ray Spectroscopy Missions Through Laboratory Astrophysics
submitted to Astro2020 Decadal Survey (2019)

Abstract: Thanks to high-resolution and non-dispersive spectrometers onboard future X-ray missions such as XRISM and Athena, we are finally poised to answer important questions about the formation and evolution of galaxies and large-scale structure. However, we currently lack an adequate understanding of many atomic processes behind the spectral features we will soon observe. Large error bars on parameters as critical as transition energies and atomic cross sections can lead to unacceptable uncertainties in the calculations of e.g., elemental abundance, velocity, and temperature. Unless we address these issues, we risk limiting the full scientific potential of these missions. Laboratory astrophysics, which comprises theoretical and experimental studies of the underlying physics behind observable astrophysical processes, is therefore central to the success of these missions.


P. Micke, S. Kühn, L. Buchauer, J. R. Harries, T. M. Bücking, K. Blaum, A. Cieluch, A. Egl, D. Hollain, S. Kraemer, T. Pfeifer, P. O. Schmidt, R. X. Schüssler, Ch. Schweiger, Th. Stöhlker, S. Sturm, R. N. Wolf, S. Bernitt, and J. R. Crespo López-Urrutia
The Heidelberg compact electron beam ion traps
Review of Scientific Instruments 89, 063109 (2018)

Abstract: Electron beam ion traps (EBITs) are ideal tools for both production and study of highly charged ions (HCIs). In order to reduce their construction, maintenance, and operation costs, we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA, and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar¹⁶⁺ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e.g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe²⁴⁺, achieving an electron-energy resolving power of E/ΔE > 1500 at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating the resonant photoexcitation of highly charged oxygen.