Mainz 2026 – scientific programme

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MO: Fachverband Molekülphysik

MO 17: Poster – Interaction with VUV and X-ray Light (joint session A/MO)

MO 17.2: Poster

Wednesday, March 4, 2026, 17:00–19:00, Philo 1. OG

Parametric Mössbauer Radiation Generated by the European XFEL Electron Beam — •Ze-an Peng, Christoph H. Keitel, and Jörg Evers — Max-Planck-Institut für Kernphysik, Heidelberg, Germany

The ultranarrow nuclear resonances of Mössbauer isotopes enable precision spectroscopy and x-ray quantum optical applications, yet they make strong resonant excitation difficult with conventional x-ray sources. Parametric x-ray radiation (PXR), produced when relativistic electrons traverse a crystal, provides a high-quality, low-divergence x- ray source. When the crystal contains Mössbauer nuclei, spectrally narrow parametric Mössbauer radiation (PMR) can be generated under suitable conditions. We develop a general dynamical diffraction theory of PMR for arbitrary emission directions, covering both the conventional diffraction geometry and the more extreme grazing specular diffraction geometry. We show that the new geometry can substantially enhance PMR intensity due to specular diffraction of the electron virtual-photon fields at the crystal surface, which allows radiation to form predominantly outside the crystal and thus avoids strong absorption. We further apply the framework to superradiant PMR (SPMR) generated by microbunched XFEL electron beams, and introduce how superradiant amplification and geometric optimization combine to boost emission. The scheme applies broadly to PXR and PMR from both incoherent continuous- wave electron beam and the XFEL electron bunches, offering a pathway toward intense, coherent, and spectrally narrow Mössbauer x-ray sources.

Keywords: Parametric x-ray radiation; XFEL electron bunch; Mössbauer resonance; X-ray diffraction dynamical theory