Abstract

We report the observation of K-shell vacancies in light elements, such as boron and carbon, by means of X-ray fluorescence using sub-10-fs-pulse-driven coherent laser harmonics as the excitation source. The experiments represent the first application of coherent water-window radiation produced by a laboratory source and are a first step towards time-resolved X-ray spectroscopy of solid-state and molecular dynamics on a sub-100-fs time scale. The inner-shell vacancies are created within less than 5 fs owing to the ultrashort duration of the excitation pulse from the few-cycle-driven harmonic source [1,2] and disappear virtually instantaneously due to ultrafast Auger relaxation, offering sub-10-fs time resolution for dynamical X-ray spectroscopy. The detection of femtosecond X-ray fluorescence in spite of the extremely low ≈10^-3 fluorescence yield of low-Z atoms suggests that already a present-day few-femtosecond high harmonic source might allow the observation of dynamical changes of K-shell chemical shifts in light elements during ultrafast molecular dynamics.

© 2000 IEEE