Observation of fluorescence from the excited atom cluster produced by irradiation with atomic-molecular photophysics extreme ultraviolet free-electron laser light derived from a short-wavelength free-electron laser

Extreme ultraviolet free-electron laser light, which is an extremely efficient photoionization and excitation source, enables the generation of high-density ions or excited atom cluster. High-density ions and excited atom cluster are expected to behave very differently from dilute systems. However, due to the high density, the influence of space charge effect is large, so charged particles cannot be used as probes. The authors focused on fluorescence relaxation, and observed the behavior of high-density excited atoms and rare gas clusters induced by extreme ultraviolet free-electron laser light. This paper introduces these results. (A.O.)