Collective dynamics of matter, which determine its optical, thermal and magnetic properties, often exhibit strong dependence on the length scale. Experimental tools for probing such dynamics in the sub-100 nm length-scales and on the relevant timescales (i.e. picosecond and sub-ps) mainly rely on the combination of ultrafast lasers and ad-hoc nanostructuration of the sample.

In this talk I will present an alternative approach, developed at the FERMI free electron laser (FEL), where the sensitivity to the sub-100 nm length-scale is obtained exploiting extreme ultraviolet transient gratings (EUV TGs) ¹. First, I will briefly address the applications of EUV TG to the investigation of the thermoelastic properties of materials on a previously inaccessible wavelength range ^2,3. Then, I will discuss the potential of EUV TGs in other contexts, beyond its original goal. Building upon the first demonstration of magnetization TGs ⁴, I will discuss the newest demonstrations of transient magnetization dynamics at the nanoscale ^5–7. To conclude, I will review further approaches exploiting the nanoscale periodically structured photoexcitation besides TG spectroscopy ⁸

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2. Foglia, L. et al. Photoacoustics 29, 100453 (2023).
3. Bencivenga, F., Capotondi, F., Foglia, L., Mincigrucci, R. & Masciovecchio, C. Adv. Phys. X 8, (2023).
4. Ksenzov, D. et al. Nano Lett. 21, 2905–2911 (2021).
5. Yao, K. et al. Nano Lett. 22, 4452–4458 (2022).
6. Steinbach, F. et al. Nano Lett. 24, 6865–6871 (2024).
7. Miedaner, P. R. et al. Sci. Adv. 10, (2024).
8. Foglia, L. et al. Nat. Commun. 15, 10742 (2024).