Thermal deformation in X-ray crystal optics in high-repetition-rate X-ray free-electron lasers can be effectively reduced by cryogenic cooling with liquid nitro­gen, and possibly by second-order correction via focusing optics.

Methods using spontaneous radiation to monitor and optimize the Aramis hard X-ray beamline are presented, together with the eight-year evolution of these improvements and the resulting record performance.

A scheme is proposed to calculate an effective fluence of a spatially non-uniform pump pulse such that the observable of interest calculated with the effective fluence is very close to the volume-integrated observable. This approach simplifies computational simulations of X-ray irradiated solids.

An injector testbed for continuous-wave free-electron lasers based on a direct current gun and an interchangeable very high frequency gun is under construction. Its physical design and performance have been studied carefully.

A high-energy-resolution X-ray spectrometer has been commissioned at the SXFEL Facility, delivering single-shot resolving power beyond 20000 to provide support for fine-tuning and optimization of the machine, during scientific research. The fine structure of the individual spiky peak in the SASE spectrum is clearly resolved to characterize the pulse length of FEL radiation.

Single-shot damage of an 200 nm-thick Au thin film is experimentally studied with a UV FEL of 121.6 nm wavelength and 2 ps pulse length. The characterized, as well as visually observed, phenomena are analyzed with multiple theoretical approaches.