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 M2,3 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.
authors: LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France.
authors: G
authors: G
authors: Lambert
authors: 1] LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France [2] Sorbonne Universités, UPMC Paris 06, UMR 7614, LCPMR, 75005 Paris, France [3] CNRS, UMR 7614, LCPMR, 75005 Paris, France.
authors: B
authors: B
authors: Vodungbo
authors: LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France.
authors: J
authors: J
authors: Gautier
authors: LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France.
authors: B
authors: B
authors: Mahieu
authors: LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France.
authors: V
authors: V
authors: Malka
authors: LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France.
authors: S
authors: S
authors: Sebban
authors: LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France.
authors: P
authors: P
authors: Zeitoun
authors: 1] Sorbonne Universités, UPMC Paris 06, UMR 7614, LCPMR, 75005 Paris, France [2] CNRS, UMR 7614, LCPMR, 75005 Paris, France.
authors: J
authors: J
authors: Luning
authors: 1] Sorbonne Universités, UPMC Paris 06, UMR 7614, LCPMR, 75005 Paris, France [2] CNRS, UMR 7614, LCPMR, 75005 Paris, France.
authors: J
authors: J
authors: Perron
authors: Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, 1, Building 2, Moscow 119991, Russia.
authors: A
authors: A
authors: Andreev
authors: 1] Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, 1, Building 2, Moscow 119991, Russia [2] National Research Centre "Kurchatov Institute", pl. Akademika Kurchatova, 1, Moscow 123182, Russia.
authors: S
authors: S
authors: Stremoukhov
authors: 1] Paul Scherrer Institute, SwissFEL, 5232 Villigen-PSI, Switzerland [2] Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors: F
authors: F
authors: Ardana-Lamas
authors: Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors: A
authors: A
authors: Dax
authors: 1] Paul Scherrer Institute, SwissFEL, 5232 Villigen-PSI, Switzerland [2] Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors: C P
authors: CP
authors: Hauri
authors: 1] LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Hunière, F-91761 Palaiseau, France [2] GoLP, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisbon, Portugal.
authors: A
authors: A
authors: Sardinha
authors: GoLP, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisbon, Portugal.
authors: M
authors: M
authors: Fajardo