Generation of bright soft X-ray pulses to watch ultrafast spin dynamics at the nanoscale

The CFEL-ATTO group collaborated in an experiment, resolved spin dynamics inside rare earth materials, using a tabletop ultrafast soft-X-ray microscope, which is relevant for future energy-efficient, high-speed spintronic applications.

Some members of the CFEL-ATTO group collaborated in spatio-temporally resolved resonant magnetic scattering experiment to probe the inner-shell 4d electrons of a rare-earth (RE) composite ferrimagnetic system using a bright >200eV soft x-ray high harmonic generation (HHG) source. This fruitful international collaboration is between Institut National de la Recherche Scientifique (INRS), TU Wien, French national synchrotron facility (SOLEIL), Fudan University and other international partners. The work has been recently published in the prestigious journal Optica.

A promising approach for speeding up data storage devices consists of switching the spin of magnetic materials with ultra-short femtosecond laser pulses. But, how the spin evolves in the nanoworld on extremely short time scales, (one millionth of one billionth of a second), has remained largely mysterious. So far, studies on this subject strongly rely on limited access large X-ray facilities such as free-electron lasers and synchrotrons.

In the work, through a careful study of the microscopic light-electron interaction and the macroscopic phase-matching in the HHG process, a new soft X-ray source based on a high energy Ytterbium laser was developed. It results in more than two orders of magnitude photon flux improvement in the soft X-ray range (>2x109 photons/s/1% bandwidth at 200 eV). With this bright source, a series of snapshot images of the nanoscale rare earth magnetic structures using femtosecond temporal and nanometer spatial resolution has been recorded. They clearly expose the fast demagnetization process, concomitant with movement of the domain periodicity on the nanometer scale. These results provide rich information on the magnetic properties that are as accurate as those obtained using large-scale X-ray facility. The results indicate rich driving mechanisms in multicomponent magnetic systems.

Considering the rapid emergence of high-power Yb lasers combined with novel nonlinear compression technology, this work paves the way to the use of table-top soft X-ray sources for many applications in condensed matter physics, life sciences, and nanotechnology.


1. Ultrafast magnetic scattering on ferrimagnets enabled by a bright Yb-based soft x-ray source

G. Fan, K. Légaré, V. Cardin, X. Xie, R. Safaei, E. Kaksis, G. Andriukaitis, A. Pugžlys, B. E. Schmidt, J. P. Wolf, M. Hehn, G. Malinowski, B. Vodungbo, E. Jal, J. Lüning, N. Jaouen, G. Giovannetti, F. Calegari, Z. Tao, A. Baltuška, F. Légaré, and T. Balčiūnas. Optica, 2022, 9(4): 399-407.


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