2021, Liu, Xuan, Merhe, Alaaeldine, Jal, Emmanuelle, Delaunay, Renaud, Jarrier, Romain, Chardonnet, Valentin, Hennes, Marcel, Chiuzbaian, Sorin G., Légaré, Katherine, Hennecke, Martin, Radu, Ilie, Von Korff Schmising, Clemens, Grunewald, Særen, Kuhlmann, Marion, Lüning, Jan, Vodungbo, Boris

In this paper, we present a new setup for the measurement of element-specific ultrafast magnetization dynamics in ferromagnetic thin films with a sub-15-fs time resolution. Our experiment relies on a split and delay approach which allows us to fully exploit the shortest X-rays pulses delivered by X-ray Free Electrons Lasers (close to the attosecond range), in an X-ray pump – X-ray probe geometry. The setup performance is demonstrated by measuring the ultrafast elemental response of Ni and Fe during demagnetization of ferromagnetic Ni and Ni80Fe20 (Permalloy) samples upon resonant excitation at the corresponding absorption edges. The transient demagnetization process is measured in both reflection and transmission geometry using, respectively, the transverse magneto-optical Kerr effect (T-MOKE) and the Faraday effect as probing mechanisms.

2017, von Korff Schmising, Clemens, Weder, David, Noll, Tino, Pfau, Bastian, Hennecke, Martin, Strüber, Christian, Radu, Ilie, Schneider, Michael, Staeck, Steffen, Günther, Christian M., Lüning, Jan, Merhe, Alaa el dine, Buck, Jens, Hartmann, Gregor, Viefhaus, Jens, Treusch, Rolf, Eisebitt, Stefan

A new device for polarization control at the free electron laser facility FLASH1 at DESY has been commissioned for user operation. The polarizer is based on phase retardation upon reflection off metallic mirrors. Its performance is characterized in three independent measurements and confirms the theoretical predictions of efficient and broadband generation of circularly polarized radiation in the extreme ultraviolet spectral range from 35 eV to 90 eV. The degree of circular polarization reaches up to 90% while maintaining high total transmission values exceeding 30%. The simple design of the device allows straightforward alignment for user operation and rapid switching between left and right circularly polarized radiation.

2020, Korff Schmising, Clemens von, Willems, Felix, Sharma, Sangeeta, Yao, Kelvin, Borchert, Martin, Hennecke, Martin, Schick, Daniel, Radu, Ilie, Strüber, Christian, Engel, Dieter W., Shokeen, Vishal, Buck, Jens, Bagschik, Kai, Viefhaus, Jens, Hartmann, Gregor, Manschwetus, Bastian, Grunewald, Soeren, Düsterer, Stefan, Jal, Emmanuelle, Vodungbo, Boris, Lüning, Jan, Eisebitt, Stefan

The vision to manipulate and control magnetism with light is driven on the one hand by fundamental questions of direct and indirect photon-spin interactions, and on the other hand by the necessity to cope with ever growing data volumes, requiring radically new approaches on how to write, read and process information. Here, we present two complementary experimental geometries to access the element-specific magnetization dynamics of complex magnetic systems via ultrafast magneto-optical spectroscopy in the extreme ultraviolet spectral range. First, we employ linearly polarized radiation of a free electron laser facility to demonstrate decoupled dynamics of the two sublattices of an FeGd alloy, a prerequisite for all-optical magnetization switching. Second, we use circularly polarized radiation generated in a laboratory-based high harmonic generation setup to show optical inter-site spin transfer in a CoPt alloy, a mechanism which only very recently has been predicted to mediate ultrafast metamagnetic phase transitions. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

2020, Schneider, Michael, Pfau, Bastian, Günther, Christian M., von Korff Schmising, Clemens, Weder, David, Geilhufe, Jan, Perron, Jonathan, Capotondi, Flavio, Pedersoli, Emanuele, Manfredda, Michele, Hennecke, Martin, Vodungbo, Boris, Lüning, Jan, Eisebitt, Stefan

We systematically study the fluence dependence of the resonant scattering cross-section from magnetic domains in Co/Pd-based multilayers. Samples are probed with single extreme ultraviolet (XUV) pulses of femtosecond duration tuned to the Co M3,2 absorption resonances using the FERMI@Elettra free-electron laser. We report quantitative data over 3 orders of magnitude in fluence, covering 16  mJ/cm2/pulse to 10 000  mJ/cm2/pulse with pulse lengths of 70 fs and 120 fs. A progressive quenching of the diffraction cross-section with fluence is observed. Compression of the same pulse energy into a shorter pulse—implying an increased XUV peak electric field—results in a reduced quenching of the resonant diffraction at the Co M3,2 edge. We conclude that the quenching effect observed for resonant scattering involving the short-lived Co 3p core vacancies is noncoherent in nature. This finding is in contrast to previous reports investigating resonant scattering involving the longer-lived Co 2p states, where stimulated emission has been found to be important. A phenomenological model based on XUV-induced ultrafast demagnetization is able to reproduce our entire set of experimental data and is found to be consistent with independent magneto-optical measurements of the demagnetization dynamics on the same samples.