Special Colloquium on the Occasion of Thomas Stöhlker's 65th Birthday

Festive Colloquium with talks by

• Gerhard G. Paulus (Institute of Optics and Quantum Electronics/Helmholtz Institute Jena)
  • Thomas Stöhlker, Helmholtz Institute Jena, and X-ray Polarimetry
    • In the beginning, there was polarimetry, X-ray polarimetry to be precise. It was X-ray polarimetry that brought me into contact with Thomas – even if it was initially more of a misunderstanding. But this contact led to the Helmholtz Institute in Jena, where Thomas has made such a significant contribution over the past 15 years. So it is only fitting that my lecture pays tribute not only to Thomas but also to X-ray polarimetry! I will therefore outline what we have achieved in X-ray polarimetry over the past 15 years. For example, an extinction ratio of 11 orders of magnitude, enough to detect the birefringence of a vacuum polarized by a laser!

and

• Paul Indelicato (Laboratoire Kastler Brossel, Université Pierre et Marie Curie, CNRS, ENS)
  • From highly charged ions spectroscopy to nuclear clocks 

    • The physics of highly charged ions has been getting a large impact on our understanding of many-body effects in atoms, bound state QED, and tests of the standard model. After the advent of beam foil spectroscopy at Van de Graff facilities in the seventies, progress came in the 80’s from the use of more advanced accelerators like cyclotrons or LINACs. The increased in precision in those experiments came also from the use of crystal spectrometers which brought they high-resolution and accuracy when calibrated x-ray standards. Yet accuracy was limited by the uncertainty on the Doppler effect. Then came the time of storage ring with the construction of the ESR at GSI. This led to a new phase, as the resolution improved, thanks to the electron cooling and metrology quality high-voltage measurements. This reduced considerably the impact of the Doppler effect. Then the use of two spectrometers on each side of the beam with a common direction allowed even more progress for the spectroscopy of few-electrons U [1]. The much-improved energies measurements in HCI allows for many new applications (e.g., ions’ high-precision clocks). And now even nuclear clocks, based on a new understanding of the nucleus-electrons interactions, are being developed. Thomas Stöhlker has been one of the scientists pushing and developing new methods to make stronger progress in the field, with a strong impact thanks to the use of GSI/FAIR storage rings and magnetic microcalorimeter which will lead to a new revolution [2]. Thomas Stöhlker is now leading a project to use highly charged ²²⁹Th ions to develop nuclear clocks. This may allow more accurate clocks and improved understanding of electron-nucleus interaction. And the comparison of several kind of high precision atomic, ion and nuclear clock will lead to new test of physics beyond the standard model by looking at possible fundamental constants’ variation with time or space.

      References

      [1]       Testing quantum electrodynamics in extreme fields using helium-like uranium, R. Loetzsch, H.F. Beyer, L. Duval et al. Nature 625, 673-678 (2024).

      [2]       Quantum Electrodynamics in Strong Electromagnetic Fields: Substate Resolved Kalpha Transition Energies in Heliumlike Uranium, P. Pfäfflein, G. Weber, S. Allgeier et al. Phys. Rev. Lett. 134, 153001 (2025).

followed by a dinner at the GSI Canteen.

REGISTRATION REQUIRED!!!

Zoom Access

https://gsi-fair.zoom.us/j/69858195293

Meeting-ID: 698 5819 5293
Kenncode: Coll-1507