Mainz 2026 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 22: Nuclear and X-Ray Quantum Optics

Q 22.1: Invited Talk

Tuesday, March 3, 2026, 11:00–11:30, P 11

Exploring nonlinear optics with x-rays — •Dietrich Krebs — Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany

Using modern synchrotron and free-electron laser (FEL) sources, it has become feasible to study a wide range of nonlinear processes in the x-ray regime. With it comes the possibility to transfer ideas from parametric nonlinear optics as well as quantum optics to shorter wavelengths, for which we will explore examples in this talk. Processes of interest comprise x-ray-optical wavemixing (XOWM) that can combine diffractive imaging capabilities with spectroscopic sensitivity for new material diagnostics. As such, we have recently demonstrated the applicability of nonlinear crystallography using x-ray-optical difference-frequency generation to spatially reconstruct the valence response in diamond at sub-Angstrom resolution. Processes deriving from spontaneous x-ray parametric down-conversion (XPDC), on the other hand, can provide access to quantum features of light-matter interaction. As an example, we showcase a series of experiments, in which we found that non-degenerate XPDC allows access to polariton-formation in the extreme-ultraviolet (EUV) and soft x-ray spectral ranges. Recent developments have also shown renewed interest to extend XPDC into the degenerate regime, aiming to produce energetically equal x-ray photon pairs as a resource of entanglement. While these examples still face substantial challenges regarding their efficiency, they provide a promising outlook for the future of x-ray quantum optics.

Keywords: nonlinear optics; x-rays; wavemixing; parametric down-conversion; crystallography