A compact and versatile tender X‐ray single‐shot spectrometer for online XFEL diagnostics

One of the remaining challenges for accurate photon diagnostics at X‐ray free‐electron lasers (FELs) is the shot‐to‐shot, non‐destructive, high‐resolution characterization of the FEL pulse spectrum at photon energies between 2 keV and 4 keV, the so‐called tender X‐ray range. Here, a spectrometer setup is reported, based on the von Hamos geometry and using elastic scattering as a fingerprint of the FEL‐generated spectrum. It is capable of pulse‐to‐pulse measurement of the spectrum with an energy resolution (Δ E / E ) of 10 −4 , within a bandwidth of 2%. The Tender X‐ray Single‐Shot Spectrometer (TXS) will grant to experimental scientists the freedom to measure the spectrum in a single‐shot measurement, keeping the transmitted beam undisturbed. It will enable single‐shot reconstructions for easier and faster data analysis.