Single resonance driven by stochastic pulses with phase fluctuations only (PDM), and phase+amplitude exponentially correlated fluctuations

Figure 6. Single resonance driven by stochastic pulses with phase fluctuations only (PDM), and phase+amplitude exponentially correlated fluctuations. The average total yield of RA electrons 〈Q₂〉 is plotted as a function of the detuning of the field from resonance, for three different values of the ratio \Omega _s^{(0)}/\Gamma _2, and for various bandwidths of the field. (a) γ = 13.33Γ₂; (b) γ = 6.67Γ₂; (c) γ = 3.33Γ₂; (d) γ = 1.67Γ₂; (e) γ = 1.11Γ₂; (f) γ = 0.83Γ₂. Other parameters: Gaussian pulse profile, Γ₂τ = 3, 2000 random pulses. The signal is symmetric with respect to Δ_s = 0, and only the part for positive Δ_s is shown.

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.