Ultrafast X-ray Spectroscopy

X-ray spectroscopic techniques rely on the element-specificity of inner-shell photoexcitation/ionization to probe electronic densities with atomic-site precision. The versatility of X-ray absorption and emission spectroscopy has made it a unique tool for determination of chemical, structural, and electronic properties of matter with successful applications in industry - for material characterization - and science– in different disciplines such as health, engineering, biology or physical chemistry.

The application of X-ray spectroscopy has continued to grow during the last half century mostly due to the impressive technological developments of accelerator-based light sources. Originally driven by the evolution of synchrotron radiation facilities, the last two decades have shown a revolution with the introduction of free electron laser (FEL) facilities. Initially these facilities employed the self-amplified spontaneous emission (SASE) technique to generate ultrashort pulses of X-ray radiation, but several developments: multi-pulse generation, seeding, and enhanced SASE open the door to the generation of fully coherent, tunable ultrashort X-ray pulse sequences. A new manifold of time-resolved X-ray spectroscopic techniques with promising applications came forward, e.g., as a tool to track the complex ultrafast dynamics triggered in photochemical processes. XFELs are not the only technological development, ultrafast x-ray pulses are now accessible with table-top laser systems using high-order harmonic generation driven by intense infrared lasers.

This collection aims to provide a description of the state-of-the-art in time-resolved X-ray spectroscopic measurements, including applications, technological developments and theoretical studies to explore ultrafast phenomena in isolated quantum systems.