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A proposal for multi-tens of GW fully coherent femtosecond soft X-ray lasers


X-ray free-electron lasers1,2 delivering up to 1 × 1013 coherent photons in femtosecond pulses are bringing about a revolution in X-ray science3,4,5. However, some plasma-based soft X-ray lasers6 are attractive because they spontaneously emit an even higher number of photons (1 × 1015), but these are emitted in incoherent and long (hundreds of picoseconds) pulses7 as a consequence of the amplification of stochastic incoherent self-emission. Previous experimental attempts to seed such amplifiers with coherent femtosecond soft X-rays resulted in as yet unexplained weak amplification of the seed and strong amplification of incoherent spontaneous emission8. Using a time-dependent Maxwell–Bloch model describing the amplification of both coherent and incoherent soft X-rays in plasma, we explain the observed inefficiency and propose a new amplification scheme based on the seeding of stretched high harmonics using a transposition of chirped pulse amplification to soft X-rays. This scheme is able to deliver 5 × 1014 fully coherent soft X-ray photons in 200 fs pulses and with a peak power of 20 GW.

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Figure 1: Temporal evolution of soft X-ray laser intensity and gain for different planes along the amplifier for single, multiple and stretched seeding.
Figure 2: Artistic view of the stretched seed amplification chain with spectro-temporal evolution of the pulse along the chain.
Figure 3: Modification of energy and spectral characteristics induced by the main amplifier.


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The authors thank G.J. Tallents, G. Mourou, J.P. Chambarret and V. Ceban for fruitful discussions. The work has been partially supported by SFINX-LASERLAB EC Seventh FP (grant agreement no. 228334) and the SHYLAX project from RTRA–Triangle de la Physique.

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The general concept was developed by P.Z., E.O. and M.F. Modelling was performed by E.O., P.V., P.Z. and T.T.T.L. Stretcher/compressor data were calculated by P.Z. and L.L., based on a model from M.P. and an idea from J.G. Detailed design and calculations were carried out with help from all authors.

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Correspondence to Ph. Zeitoun.

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The authors declare no competing financial interests.

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Oliva, E., Fajardo, M., Li, L. et al. A proposal for multi-tens of GW fully coherent femtosecond soft X-ray lasers. Nature Photon 6, 764–767 (2012).

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