Neon’s electronic blueprint

The European XFEL, the 3.4-km-long x-ray free-electron laser facility in Schenefeld, Germany, can generate some 27 000 x-ray flashes per second, with a brilliance about a billion times that of the best conventional x-ray sources. The picture here shows the inside of the Atomic-like Quantum Systems station, one of three stations of the Small Quantum Systems instrument. The wires at the top of the image belong to a velocity-map-imaging spectrometer; the conical objects near the bottom are the electron time-of-flight spectrometers, which provide the capability to measure the energy of electrons that carry information about an atom’s transient states.

Tommaso Mazza, a research scientist at the facility, and his colleagues investigated ultrafast decaying states in the electronic structure of a neon atom before any relaxation of the system occurred. The neon atom was first photoionized by a single x-ray photon. That kicked one electron out of the atomic core and left a hole. Then a second x-ray photon from the same pulse probed the transient electronic state of the core-excited atom, which lasted for only about 2.5 femtoseconds. With high-resolution electron spectroscopy, the researchers then observed Rydberg resonances and unraveled the details of the subsequent decay of the hollow atom. (Image courtesy of the European XFEL; T. Mazza et al., Phys. Rev. X 10, 041056, 2020, doi:10.1103/PhysRevX.10.04105 .)