Speaker
Description
Capturing movies of ultrafast processes in nanomatter has been a driving force for the development of X-ray Free Electron Lasers (XFELs). Since the first demonstration of Coherent Diffraction Imaging (CDI) at an XFEL facility [1], the technique has moved from a niche proof-of-concept to a well-established, standard tool, allowing for snapshot imaging of fragile and transient structures, from quantum vortices in superfluid helium nanodroplets [2] to light-induced ultrafast melting [3]. Alongside the consolidation of established techniques, recent years have seen a substantial development of new operational modes for XFELs, opening exciting possibilities and calling for the development of novel experimental methods. Among these, modern XFELs are now capable of producing ultrashort, ultrabright pairs of X-ray pulses of two distinct "colors" (i.e., photon energies). The possibility of precisely controlling the time delay between the two colors down to the femtosecond regime allows for probing the same system at two different points in time, even down to the natural timescales of electron dynamics [4]. In this talk, we describe how two-color pulses can be combined with CDI experiments to capture two time-delayed snapshots of the same sample through a new technique called Dichography [5]. In particular, we show results on two-color diffraction patterns acquired at the European XFEL, where two images of the same xenon-doped superfluid helium nanodroplet, separated in time by up to 750 fs, are successfully retrieved despite demanding experimental conditions. While further improvements to both instrumentation and data analysis are necessary to maximize the resolution of the technique, the exciting possibility of two-color diffraction imaging at XFELs, so far considered unviable, opens a new research path for recording movies of ultrafast structural and electron dynamics at the nanoscale.
- Chapman, Henry N., et al. "Femtosecond diffractive imaging with a soft-X-ray free-electron laser." Nature Physics 2.12 (2006): 839-843.
- Gessner, Oliver, and Andrey F. Vilesov. "Imaging quantum vortices in superfluid helium droplets." Annual review of physical chemistry 70.1 (2019): 173-198.
- Dold, Simon, et al. "Melting, bubblelike expansion, and explosion of superheated plasmonic nanoparticles." Physical review letters 134.13 (2025): 136101.
- Hecht, Linos, et al. "Two-Color X-Ray Coherent Diffraction Imaging of Helium Nanodroplets." arXiv preprint arXiv:2508.19991 (2025).
- Hecht, Linos, et al. "Dichography: two-frame ultrafast imaging from a single diffraction pattern." Nature Communications, in press (2026).
| Scientific Topics | Imaging |
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