Nanoscale transient gratings excited and probed by extreme ultraviolet femtosecond pulses

Abstract

Advances in developing ultrafast coherent sources operating at extreme ultraviolet (EUV) and x-ray wavelengths allow the extension of nonlinear optical techniques to shorter wavelengths. Here, we describe EUV transient grating spectroscopy, in which two crossed femtosecond EUV pulses produce spatially periodic nanoscale excitations in the sample and their dynamics is probed via diffraction of a third time-delayed EUV pulse. The use of radiation with wavelengths down to 13.3 nm allowed us to produce transient gratings with periods as short as 28 nm and observe thermal and coherent phonon dynamics in crystalline silicon and amorphous silicon nitride. This approach allows measurements of thermal transport on the ~10-nm scale, where the two samples show different heat transport regimes, and can be applied to study other phenomena showing nontrivial behaviors at the nanoscale, such as structural relaxations in complex liquids and ultrafast magnetic dynamics.

Femtosecond laser driven precessing magnetic gratings

“…A natural extension of the method would be excitation through extreme ultraviolet (EUV) wavelengths, facilitating optical gratings on a few nanometer scale. 41,42 The TG facilitates the formation of magnetic domains with tunable nanoscale dimensions, which may allow the study of magnetic dynamics at dimensions comparable to the intrinsic scales of domain walls or other magnetic structures, such as vortices or skyrmions. Furthermore, analysis of local temperatures and thermal diffusion at combined nanometer and picosecond res- olutions in materials and devices is challenging.…”

“…1,2 This technique offers opportunities to study the interaction of light and matter under tailored periodic spatial excitation conditions. The spatial excitation period can be tuned from micrometers, using optical wavelengths, to tens of nanometers by means of extreme ultraviolet (EUV) light 3,5 or even X-rays. [6][7][8][9] The technique has been extensively applied to a diverse set of material processes occurring on an ultrafast time scale including the generation of surface acoustic waves, 1,3 phonon polariton excitation, 10 quasi-particle diffusion, 11 molecular diffusion, 12 thermal transport, 4,13 charge density waves, 14 and laserplasma interactions.…”

Accessing temperature waves: A dispersion relation perspective

“…in between the oscillation period 2π/ω 1 (k Qmax ) and Q max times its value). In order to impulsively trigger the best oscillating temperature mode, a transient grating with P =2π/k Qmax = 1.5 µm is thus required, a figure within reach of present TTG spectroscopy [64,65].…”

Non-linear self-driven spectral tuning of Extreme Ultraviolet Femtosecond Pulses in monoatomic materials

“…Exploring novel non-linear light-matter interactions in EUV and X-ray ranges, enabled by FEL and HHG sources, is recently attracting a lot of interest, based on the opportunity to design new spectroscopic approaches [5][6][7] and to exploit NLEs in a high-energy regime [8][9][10][11][12][13][14][15][16] . For example, theoretical and experimental efforts have been devoted to probe the effects of the core dynamics on the absorption properties of the sample, monitoring the photo-induced modification to the absorption spectra of materials pumped in the XUV and EUV ranges, either by the strong field of a single probe pulse 8,12,17 or by using an additional pump pulse 18 .…”