An atomic transition pertaining to a sub-valence electron, driven by chaotic SASE-FEL pulses

Figure 4. An atomic transition pertaining to a sub-valence electron, driven by chaotic SASE-FEL pulses. The resulting inner-shell vacancy in the excited atom decays with rate Γ₂.

Abstract

Motivated by recent experiments pertaining to the interaction of weak SASE-free-electron-laser (FEL) pulses with atoms and molecules, we investigate the conditions under which such interactions can be described in the framework of a simple phase-diffusion model with decorrelated atom–field dynamics. The nature of the fluctuations that are inevitably present in SASE-FEL pulses is shown to play a pivotal role in the success of the decorrelation. Our analysis is performed in connection with specific recent experimental results from FLASH in the soft x-ray regime.