As in figure 6, for phase+amplitude Gaussian-correlated fluctuations and bandwidths: (a) γ = 15.70Γ₂; (b) γ = 7.85Γ₂; (c) γ = 3.92Γ₂; (d) γ = 1.96Γ₂; (e) γ = 1.31Γ₂; (f) γ = 0.98Γ₂

Figure 7. As in figure 6, for phase+amplitude Gaussian-correlated fluctuations and bandwidths: (a) γ = 15.70Γ₂; (b) γ = 7.85Γ₂; (c) γ = 3.92Γ₂; (d) γ = 1.96Γ₂; (e) γ = 1.31Γ₂; (f) γ = 0.98Γ₂.

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.