3.2 Solids and Nanostructures: Electrons, Spins, and Phonons

T1: Magnetism and transient electronic structure

Experimental Methods

We use intense and ultrashort laser pulses (λ = 800 nm, E = 4.5 mJ at 3 kHz, Δt < 25 fs) to generate high harmonic radiation in the extreme ultraviolet (XUV) spectral range up to approximately 100 eV. In a pump-probe measurement scheme we then employ magnetic dichroism to probe the femtosecond magnetic response after optical excitation. This allows simultaneous access to the element-specific magnetization dynamics in complex and multi-element magnetic systems. A normalization scheme yields an excellent signal to noise ratio within a short measurement time. The sample environment includes an external magnetic field as well as a closed cycle cryostat with a temperature range between < 10 K and 700 K.

An additional beamline has been setup for small angle X-ray scattering and coherent imaging experiments (with project 3.3). We select a single harmonic via highly reflective multilayer mirrors and record far field diffraction patterns of the target via a in-vacuum CCD camera.

For more details please refer to

K. Yao et al., A tabletop setup for ultrafast helicity-dependent and element-specific absorption spectroscopy and scattering in the extreme ultraviolet spectral range Rev. Sci. Instrum. 91, 093001 (2020).

Recent articles on the spectroscopic techniques in the XUV spectral range for accessing ultrafast magnetization dynamics include:

J. Richter et al., Relationship between magnetic asymmetry and magnetization in ultrafast transverse magneto-optical Kerr effect spectroscopy in the extreme ultraviolet spectral range, Physical Review B 109  184440 (2024).

J. Richter et al., Spectroscopic probe of ultrafast magnetization dynamics in the extreme ultraviolet spectral range, Physical Review B 111 214423 (2025). 

We have recently started to perform experiments at higher photon energies in collaboration with the NanoMovie activities, starting with investigations of ultrafast dynamics of rare earth materials at 4d to 4f transitions around 150 eV.

M. van Mörbeck-Bock et al., Proceedings Volume 11777, High Power Lasers and Applications; 117770C (2021).

M. Hennecke et al., Ultrafast element- and depth-resolved magnetization dynamics probed by transverse magneto-optical Kerr effect spectroscopy in the soft x-ray range, Phys. Rev. Research 4, L022062 (2022) .

M. Hennecke et al., Transient domain boundary drives ultrafast magnetisation reversal, Nature Communications 16  8233 (2025).

To investiage all-optical switching we have set up an time resolving Kerr microscope with femtosecond temporal and micrometer spatial resolution. The system is driven by a fiber-based laser amplifier (Satsuma HP, Amplitude systems) with variable repetition rates between 500 kHz and single shot, pulse energies of up to 20 µJ and a pulse duration of < 250 fs.

For more details please refer to

F. Steinbach et al., Wide-field magneto-optical microscope to access quantitative magnetization dynamics with femtosecond temporal and sub-micrometer spatial resolution, Journal of Applied Physics 130, 083905 (2021).

F. Steinbach et al., Accelerating double pulse all-optical write/erase cycles in metallic ferrimagnets, Applied Physics Letter 120, 112406 (2022).

D. Schick et al., High-speed spatial encoding of modulated pump–probe signals with slow area detectors, Meas. Sci. Technol. 32 025901 (2021).

D. Metternich et al., Defects in magnetic domain walls after single-shot all-optical switching, Structural Dynamics 12 024504 (2025).