@article{4f879211c1f146bd9a9ee04fc10beddb,
title = "Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources",
abstract = "Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far. We here show how this limitation is overcome by using a cross-polarized two-colour laser field. With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics. To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M-2,M-3 absorption edge around 67 eV. There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials.",
author = "G. Lambert and B. Vodungbo and J. Gautier and B. Mahieu and V. Malka and S. Sebban and P. Zeitoun and J. Luning and J. Perron and A. Andreev and S. Stremoukhov and F. Ardana-Lamas and A. Dax and Hauri, {C. P.} and A. Sardinha and M. Fajardo",
note = "The experiments have been performed through LASERLAB contracts (grant agreements no. 1465, no. 1566 and no. 284464). The work was supported by the ERC X-five (contract number 339128), by the French Agence Nationale de la Recherche (ANR) under grant NT09491966 (FEMTO-X-MAG) {\textquoteleft}Nanoscale imaging of femtosecond magnetization dynamics by the scattering of coherent soft X-ray laser harmonics{\textquoteright} and by the Russian Foundation for Basic Research (grants no. 12-02-00969, 15-02-04352). C.P.H. and F.A.-L. acknowledge support from SNF (PP00P2_150732) and association to NCCR-MUST. M.F. and A.S. also thank the FCT—Portuguese Foundation for Science and Technology PTDC/FIS/112392/2009. P.Z. thanks the support from the COST action MP1203. G.L. and B.V. conducted both the experiments and analysed the data. G.L., P.Z. and M.F. proposed the concept of the polarization experiment. J.G. and A.S. helped in designing the polarization experiment. B.V. and J.L. proposed the XMCD experiment. F.A.-L., A.D. B.M. and C.P.H. took part in the XMCD experiments. J.P. prepared the nickel sample. M.F., P.Z., J.L., S.Se. and V.M. supervised the project. S.St. and A.A. conducted the theoretical investigations leading to simulations, which oriented the experimental work. All the authors discussed and contributed to the manuscript.",
year = "2015",
month = feb,
day = "4",
doi = "https://doi.org/10.1038/ncomms7167",
language = "الإنجليزيّة",
volume = "6",
journal = "Nature Communications",
issn = "2041-1723",
publisher = "Nature Research",
}