Free-electron lasers producing ultrashort pulses with high peak power promise to extend ultrafast non-linear spectroscopic techniques into the extreme-ultraviolet–X-ray regime. Key aspects are the synchronization between pump and probe, and the control of the pulse properties (duration, intensity and coherence). Externally seeded free-electron lasers produce coherent pulses that can be synchronized with femtosecond accuracy. An important goal is to shorten the pulse duration, but the simple approach of shortening the seed is not sufficient because of the finite-gain bandwidth of the conversion process. An alternative is the amplification of a soliton in a multistage, superradiant cascade: here, we demonstrate the generation of few-femtosecond extreme-ultraviolet pulses, whose duration we measure by autocorrelation. We achieve pulses four times shorter, and with a higher peak power, than in the standard high-gain harmonic generation mode and we prove that the pulse duration matches the Fourier transform limit of the spectral intensity distribution.
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Source data are provided with this paper. The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
The simulation reported in Fig. 4 was carried out with version 2 and version 4 of the code GENESIS 1.3 available at http://genesis.web.psi.ch and https://github.com/svenreiche/Genesis-1.3-Version4.
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We acknowledge S. Reiche for helpful discussions on bandwidth issues in the simulation of a multistage cascade in GENESIS 1.3. We are also grateful to the whole FERMI team for the dedicated work and support during this experiment.
The authors declare no competing interests.
Peer review information Nature Photonics thanks Agostino Marinelli and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Data file after analysis for Fig. 2.
Data file after analysis for Fig. 3.
Data file after analysis for Fig. 4.
Zip file containing 7 + 7 HDF5 datasets of acquisitions of the FEL+linac parameters in SRC and HGHG configurations (Fig. 5a and Fig. 5b). Each file corresponds to a different tuning of the resonance in the final amplifier in the two configurations, SRC (Fig. 5a) and HGHG (Fig. 5b). The spectral raw data, to be averaged to prepare the figures, are in the folder /real time/spectrometer PRESTO/GetSpectrum. Each HDF5 file contains all the linac/undulator/beam data from a machine snapshot taken before the acquisition.
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Mirian, N.S., Di Fraia, M., Spampinati, S. et al. Generation and measurement of intense few-femtosecond superradiant extreme-ultraviolet free-electron laser pulses. Nat. Photon. 15, 523–529 (2021). https://doi.org/10.1038/s41566-021-00815-w