Self-induced splitting of x-ray emission lines

XUV superfluorescence from helium gas in the paraxial three-dimensional approximation

“…Figure 3 the target for different backing pressures after the onset of saturation. Broadening of the spectral line is caused by the Autler-Townes effect and is characteristic of the saturation regime of superfluorescence [9,22]; however, its asymmetry is specific to the presented case. In part, the asymmetric profile is a consequence of the fact that radiation stems from an autoionizing resonance.…”

“…The ground state of He + can be further photoionized to He 2+ by the strong pump pulse, making the spatiotemporal dependence of population inversion more complex. The emitted field is delayed with respect to the pump pulse, as amplification requires some time to build up [9]. Since Fig.…”

“…The energy of photons emitted on the |i -| f transition is relatively close to the 40.8 eV energy of the 1s-2p transition in He + with a 6.6 μeV natural width. The ground state of He + (denoted by |a ) is strongly populated by autoionization of the doubly excited state, so in the saturation regime, where the spectral width of emitted radiation is expected to increase [9], significant field absorption due to the He + 1s-2p transition could occur and the corresponding resonant coupling must be considered by the model. Spontaneous emission on this transition is neglected, since the He + 2p excited state (|b ) has a lifetime of 100 ps.…”

“…Since the emitted light pulses have high longitudinal coherence and a duration that is comparable to that of FEL pulses [8,9], there has been interest in employing superfluorescence as the basis for new implementations of x-ray lasers [10]. However, designing such elaborate instruments requires reliable theoretical predictions.…”

“…However, designing such elaborate instruments requires reliable theoretical predictions. Modeling of superfluorescence is an intricate problem, which has been extensively investigated in the optical domain [4], but has recently also received attention at shorter wavelengths [8,9,11]. Despite the progress in the theoretical description of XUV and x-ray superfluorescence, the agreement between predictions and experimental results is still only qualitative.…”