Statistics of the generated pulses

<p><strong>Figure 2.</strong> Statistics of the generated pulses. Typical distributions of (a) the instantaneous intensity \tilde{I}(t)=I_s(t)/\langle I_s(t)\rangle at <em>t</em> − <em>t</em>₀ = τ/2 and (b) the energy per pulse \tilde{W}=W_s/\langle W_s\rangle. The dashed lines are fits according to the expected PDFs (see the text). Other parameters: τ = 10 fs, σ_ω = 0.25 rad fs⁻¹, 10³ trajectories.</p> <p><strong>Abstract</strong></p> <p>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.