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2015: Generation of elliptically polarized high harmonics

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Physicists from M.V. Lomonosov MSU in collaboration with colleagues from France, Switzerland and Portugal demonstrated the method of generating elliptically polarized high-order harmonics in atomic gases interacting with cross-polarized two-colour laser fields. This phenomenon opens up the wide perspectives for the development of polarization sensitive methods of UV and X-ray spectroscopy.

Recent advances in high-harmonic generation gave rise to the usage of generated UV and X-ray radiations for a number of practical applications. Until recently, these sources enable to produce the linearly polarized radiation mainly, because the yield of generation of elliptically polarized high harmonics has been too low.

The research performed by collaboration of Laboratoire d’Optique Appliquée and Université Paris-Sorbonne (France), Paul Scherrer Institute and Ecole Polytechnique Fédérale de Lausanne (Switzerland), Universidade de Lisboa (Portugal) and the Faculty of Physics of M.V. Lomonosov Moscow State University have demonstrated the high efficiency of generation of elliptically polarized high harmonics. A relatively simple optical setup to produce the cross-polarized two-colour laser fields was proposed. The second harmonic crystal is inserted into the laser beam at fundamental frequency and then the two-color field is focused into neon gas medium in which, due to the effect of high-order harmonic generation, the elliptically polarized coherent pulsed X-ray radiation is generated. To demonstrate the potential of elliptically polarized X-rays in spectroscopic studies the magnetic circular dichroism effect in nickel at the M2,3 absorption edge was investigated. The obtained results show the high potentiality of high optical harmonics in studying the ultrafast magnetization dynamics of individual components in complex materials.

The results of this work have been published in the paper: G. Lambert, B. Vodungbo, J. Gautier, B. Mahieu, V. Malka, S. Sebban, P. Zeitoun, J. Luning, J. Perron, A. Andreev, S. Stremoukhov, F. Ardana-Lamas, A. Dax, C. P. Hauri, A. Sardinha, M. Fajardo, “Towards enabling femtosecond helicity-dependant spectroscopy with high-harmonic sources”, Nature Communications 6, 6167 (2015).