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PUBLISHED ONLINE: 16 NOVEMBER 2015 | http://dx.doi.org/10.1038/nphoton.2015.225
Web End =DOI: 10.1038/NPHOTON.2015.225
Table-top femtosecond soft X-ray laser by collisional ionization gating
A. Depresseux1, E. Oliva2, J. Gautier1, F. Tissandier1, J. Nejdl3, M. Kozlova3, G. Maynard2, J. P. Goddet1,A. Tafzi1, A. Lifschitz1, H. T. Kim4,5, S. Jacquemot6,7, V. Malka1, K. Ta Phuoc1, C. Thaury1, P. Rousseau1,G. Iaquaniello1, T. Lefrou1, A. Flacco1, B. Vodungbo1, G. Lambert1, A. Rousse1, P. Zeitoun1 and S. Sebban1*
The advent of X-ray free-electron lasers has granted researchers an unprecedented access to the ultrafast dynamics of matter on the nanometre scale13. 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 eld 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 cm2) guided in an optically pre-formed plasma waveguide. For electron densities that ranged from 3 1018 cm3 to 1.2 1020 cm3, 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.
In plasma-based SXRL systems, the amplifying medium is a hot, highly charged plasma generated by the interaction of an intense laser pulse with a solid8 or a gas9 target. Hitherto, in all SXRL ampliers that operate at saturation, a population inversion between the levels of the lasing ion is induced by electron-collisional excitation, which results in a strong amplication of spontaneous emission (ASE) down to 3.56 nm (ref. 10) with a high temporal coherence11. When seeded with a high-order harmonic (HH) beam, the generated soft X-ray beam exhibits excellent spatial properties6 and an adjustable linear polarization12. However, all previous attempts to shorten the duration of plasma-based SXRLs below 1 ps have failed13,14, with the fundamental lower limit
governed by the very narrow gain bandwidth of collisionally pumped plasma ampliers. Therefore, a wealth of phenomena that occur on femtosecond timescales, such as molecular dynamics2 or lattice vibrations3, unfortunately remained out of reach for...