Description
The extreme ultraviolet transient grating approach (EUV TG) was conceived for probing nanoscale collective dynamics in condensed matter, such as thermal relaxations, phonons and magnons [1-3]. In recent years, the “structured” (i.e. spatially sinusoidal) excitation pattern provided by the EUV TG “pump” was used in different contexts, ranging from nanoscale all-optical magnetic switching [4] to self-diffraction spectroscopy [5].
Following the first demonstration of TG excitation by hard X-ray pulses [6], relevant efforts in extending the TG approach in the hard X-ray regime are being spent in many XFEL facilities, with encouraging results [7]. Indeed, X-ray TG offers several advantages with respect to EUV TG: (i) the possibility of accessing shorter periods of the TG (because of the shorter wavelength of the excitation), (ii) the much wider range of core resonances exploitable by hard X-ray spectroscopy and (iii) the higher penetration depth. The latter aspect directly reflects in a large increase in the expected signal; it also permits both to overcome severe sample-related limitations (e.g. the need of very thin samples for probing bulk responses) and to implement sample environments not feasible with EUV photons (e.g. high-pressure cells).
In this talk I will provide an overview of our efforts in extending the EUV TG approach beyond the study of collective dynamics at the nanoscale, with emphasis on the opportunities offered by the exploitation of EUV and X-ray spectroscopy. In addition, I will present some considerations about the range of feasibility of X-ray TG, related to the excitation and detection processes.
References
[1] F. Bencivenga et al., “Nanoscale transient gratings excited and probed by extreme ultraviolet femtosecond pulses”, Science Advances 5, eaaw5805 (2019).
[2] L. Foglia, R. Mincigrucci et al., “Extreme ultraviolet transient gratings: A tool for nanoscale photoacoustics”, Photoacoustics 29, 100453 (2023); M. Hadi et al., “The effect of echoes interference on phonon attenuation in a nanophononic membrane”, Nat. Commun. 15, 1317 (2024).
[3] P. Miedaner et al., “Excitation and detection of coherent nanoscale spin waves via extreme ultraviolet transient gratings”, Science Advances 10, eadp6015 (2024).
[4] K. Yao et al., “All-Optical Switching on the Nanometer Scale Excited and Probed with Femtosecond Extreme Ultraviolet Pulses”, Nano Lett. 22, 4452-4458 (2022); F. Steinback et al. “Exploring the Fundamental Spatial Limits of Magnetic All-Optical Switching”, Nano Letters 24, 6865–6871 (2024).
[5] A.A. Maznev et al., “Resonant Self-Diffraction of Femtosecond Extreme Ultraviolet Pulses in Cobalt”, submitted (preprint available here: https://arxiv.org/abs/2505.07168); L. Foglia et al., “Time-domain resonant self-diffraction spectroscopy in the extreme ultraviolet”, in preparation.
[6] J.R. Rouxel et al., “Hard X-ray transient grating spectroscopy on bismuth germinate”, Nature Photonics 15, 499–503 (2021).
[7] E. Ferrari et al., “All hard X-ray transient grating spectroscopy”, Communications Physics 8, 257 (2025); P. Miedaner et al., “Spin waves excited by hard x-ray transient gratings”, Physical Review Letters, in press.
