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

2013-08-13T00:00:00Z (GMT) by G M Nikolopoulos P Lambropoulos
<p><strong>Figure 6.</strong> Single resonance driven by stochastic pulses with phase fluctuations only (PDM), and phase+amplitude exponentially correlated fluctuations. The average total yield of RA electrons 〈<em>Q</em><sub>2</sub>〉 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 = 13.33Γ<sub>2</sub>; (b) γ = 6.67Γ<sub>2</sub>; (c) γ = 3.33Γ<sub>2</sub>; (d) γ = 1.67Γ<sub>2</sub>; (e) γ = 1.11Γ<sub>2</sub>; (f) γ = 0.83Γ<sub>2</sub>. Other parameters: Gaussian pulse profile, Γ<sub>2</sub>τ = 3, 2000 random pulses. The signal is symmetric with respect to Δ<sub><em>s</em></sub> = 0, and only the part for positive Δ<sub><em>s</em></sub> is shown.</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.</p>