Speaker
Description
We investigate attosecond spike formation in an x-ray free-electron laser driven by sign-reversing chirped undulator tapering in a strongly non-adiabatic regime. When the total detuning changes appreciably over one gain length, the longitudinal dynamics is most transparently described through slice-resolved bunching evolution. We introduce a reduced physical picture that organizes the process into three stages: chirp-filtered onset of microbunching near selected modulation slices, asymmetric dephasing across the modulation, and delayed post-reversal emission from comparatively fresh slices. Time-dependent three-dimensional simulations with Athos-like soft-x-ray parameters support this picture and show localized soft-x-ray spike trains with FWHM durations of about 200–300 as and peak powers in the tens-of-gigawatts range, while reference configurations without chirp-based tapering remain multi-femtosecond. The same framework also clarifies an important boundary case: strongly nonlinear sawtooth modulation does not generate isolated spikes under the simulated conditions studied here.
Funding Agency
No external funding to declare.
Footnotes
- J. Duris et al., Nat. Photonics 14, 30 (2020)
** P. Baxevanis et al., Phys. Rev. Accel. Beams 21, 110702 (2018)
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