Speaker
Filippo Bencivenga
(Elettra-Sincrotrone Trieste)
Description
Fully coherent ultrafast pulses in the extreme ultraviolet (EUV) and soft x-ray spectral range are nowadays available at seeded free electron laser (FEL) facilities, such as FERMI (Trieste, Italy). This new generation of light sources has allowed the development of an experimental approach based on the exploitation of the four-wave-mixing response, in the so-called transient grating (TG) scheme [1,2]. EUV TG can be used to probe several types of dynamical processes and, recently, has been implemented with FEL-pump/FEL-probe capabilities at the TIMER beamline [3,4]. This latter development removed the main limitation of EUV-optical TG experiments [1,2], that was the access to a length-scale range shorter than optical wavelengths (< 1 μm). Therefore, TG experiments fully based on EUV pulses are now able to explore the mesoscopic (10’s of nm) range, hardly accessible by other means.
In this presentation we report on these new experimental capabilities and on the first experimental projects, carried out in close collaboration with the users. As a result, phonon dynamics down to 24 nm wavelength and thermal responses down to a sub-10 nm thermal transport distances were observed in a number of samples [4-6]. In such a regime we found that the thermal transport process in crystalline samples shows a strongly non-diffusive nature, while in amorphous silicon nitride it is still compatible with regular thermal diffusion [4]. Applications of the EUV TG approach can also be envisioned in other research fields, as for instance in the study of mesoscopic structural relaxations in liquids or nanoscale magnetic dynamics; the latter was demonstrated in recent experiments [6,7].
Finally, it is worth stressing that these data represent unique experimental evidences of time-resolved four-wave-mixing processes exclusively driven by EUV pulses [6,7]. This is a remarkable advance in nonlinear optics and holds great potential for a wider class of nonlinear x-ray experiments, so far conceived only on theoretical grounds.
References
[1] F. Bencivenga et al., Nature 520, 205 (2015)
[2] A.A. Maznev et al., Appl. Phys. Lett. 113, 221905 (2018)
[3] L. Foglia et al., Phys. Rev. Lett. 120, 263901 (2018)
[4] F. Bencivenga et al., Science Advances 5, eaaw5805 (2019)
[5] D. Naumenko*, R. Mincigrucci* et al., ACS Appl. Nano Mater. 2, 5132 (2019)
[6] G. Monaco, K.A. Nelson, A.A. Maznev unpublished
[7] D. Ksenzov et al., in preparation
Primary author
Filippo Bencivenga
(Elettra-Sincrotrone Trieste)
