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Table-top femtosecond soft X-ray laser by collisional ionization gating


The advent of X-ray free-electron lasers has granted researchers an unprecedented access to the ultrafast dynamics of matter on the nanometre scale1,2,3. Aside from being compact, seeded plasma-based soft X-ray lasers (SXRLs) turn out to be enticing as photon-rich4 sources (up to 1015 per pulse) that display high-quality optical properties5,6. Hitherto, the duration of these sources was limited to the picosecond range7, which consequently restricts the field of applications. This bottleneck was overcome by gating the gain through ultrafast collisional ionization in a high-density plasma generated by an ultraintense infrared pulse (a few 1018 W cm−2) guided in an optically pre-formed plasma waveguide. For electron densities that ranged from 3 × 1018 cm−3 to 1.2 × 1020 cm−3, the gain duration was measured to drop from 7 ps to an unprecedented value of about 450 fs, which paves the way to compact and ultrafast SXRL beams with performances previously only accessible in large-scale facilities.

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Figure 1: Computed temporal dependence of the average charge state and gain coefficient of a krypton-plasma amplifier for ne = 6 × 1018 cm−3 (green), ne = 1.2 × 1020 cm−3 (blue) and ne = 4 × 1020 cm−3 (red).
Figure 2: Schematic of the experimental arrangement.
Figure 3: Far-field beam profiles.
Figure 4: Temporal dependence of the amplification factor with respect to the seeding delay.
Figure 5: Simulated temporal profiles of the amplified SXRL for the set of studied densities and a prospective one for ne = 4 × 1020 cm−3 (red).


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We thank J. L. Charles for his technical support. This work was backed by the Agence Nationale de la Recherche through projects ROLEX ANR-06-BLAN-04 023 01 and ANR-10-EQPX-25, and by the European Research Council through the X-five project (Contract No. 339128). We acknowledge funding from project ECOP (Grant No. CZ.1.07/2.3.00/20.0279 and No. CZ.1.07/2.3.00/30.005) and ANR-11-IDEX-0003-02. H.T.K. was supported by the Institute for Basic Science (IBS-CA1306). Finally, we also thank SourceLAB for its contribution to the development of the high-density gas-jet system.

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Authors and Affiliations



S.S. proposed the experiment. S.S., J.G, F.T. and A.D. designed and built the set-up. G.M. developed the code OFI-0D. E.O., G.M. and A.L. performed the numerical simulations. J.P.G. and A.T. designed, built and operated the upgraded laser system of ‘Salle Jaune’. K.T.P., C.T. and P.R. provided support for the operation of the facilities. A.F. developed a phase reconstruction and Abel inversion software for the electron-density diagnostic. All the authors contributed to the data analysis and the writing of the paper. P.Z., S.J., V.M. and A.R. supported the project.

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Correspondence to S. Sebban.

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The authors declare no competing financial interests.

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Depresseux, A., Oliva, E., Gautier, J. et al. Table-top femtosecond soft X-ray laser by collisional ionization gating. Nature Photon 9, 817–821 (2015).

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