Speaker
Description
Ultrafast optical laser-based techniques have enabled the probing of atomistic processes at their intrinsic temporal scales with femto- and attosecond resolution.
However, the long wavelengths of optical lasers have prevented their interrogation and manipulation with nanoscale spatial specificity.
Advances in hard X-ray free-electron lasers have enabled progress in developing X-ray transient grating spectroscopy — a technique that aims to coherently control elementary excitations with nanoscale X-ray standing waves.
Thus far, the realization of this technique at the nanoscale has been a challenge.
Here we demonstrate X-ray transient grating spectroscopy with spatial periods of the order of 10 nm via sub-femtosecond synchronization of two hard X-ray pump pulses at a precisely controlled crossing angle.
This creates a thermal grating and preferentially excites coherent longitudinal acoustic phonon modes with the transient grating wavevector.
Probing with a third, variably delayed X-ray pulse with the same photon energy, time-and-wavevector resolved measurements of the induced scattering intensity modulation provide evidence of ballistic thermal transport at nanometer scales.
These results highlight the potential of X-ray transient grating as a powerful platform for studying nanoscale transport in condensed matter and the coherent control of nanoscale dynamics.
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