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.

2018, Kluge, Thomas, Rödel, Melanie, Metzkes-Ng, Josefine, Pelka, Alexander, Laso Garcia, Alejandro, Prencipe, Irene, Rehwald, Martin, Nakatsutsumi, Motoaki, McBride, Emma E., Schönherr, Tommy, Garten, Marco, Hartley, Nicholas J., Zacharias, Malte, Grenzer, Jörg, Erbe, Artur, Georgiev, Yordan M., Galtier, Eric, Nam, Inhyuk, Lee, Hae Ja, Glenzer, Siegfried, Bussmann, Michael, Gutt, Christian, Zeil, Karl, Rödel, Christian, Hübner, Uwe, Schramm, Ulrich, Cowan, Thomas E.

The complex physics of the interaction between short-pulse ultrahigh-intensity lasers and solids is so far difficult to access experimentally, and the development of compact laser-based next-generation secondary radiation sources, e.g., for tumor therapy, laboratory astrophysics, and fusion, is hindered by the lack of diagnostic capabilities to probe the complex electron dynamics and competing instabilities. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small-angle x-ray scattering of femtosecond x-ray free-electron laser pulses facilitates new capabilities for direct in situ characterization of intense short-pulse laser-plasma interactions at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short-pulse high-intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the preinscribed grating, due to plasma expansion. The density maxima are interleaved, forming a double frequency grating in x-ray free-electron laser projection for a short time, which is a hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.