Credit: Theodor Holstad et al.
Danish and American researchers have successfully captured soundwaves traveling through a crystal. The researchers utilized X-ray microscopy to image acoustic waves within mm-sized crystals and with subpicosecond resolution.
Sound waves travel through materials very rapidly. Often only being present for less than a millisecond, imaging these sound waves has proved difficult until now. Recent findings published in PNAS, outline a method for imaging with excellent resolution that is also non-destructive. “We want to see these changes in 3D, but until now, it couldn’t be done fast enough or without damaging the crystals. Our new technology can do it faster and non-invasively and will work for many crystals,” Said Professor Henning Friis Poulsen from DTU Physics.
Poulsen adds: “To do imaging at the speed of sound, it was necessary to build an entirely new microscope at the end of a 3 km long “X-ray free-electron laser” (XFEL). It is not a given that you’ll succeed when aiming a 3 km long X-ray source through multiple lenses and onto a sample that is 1 mm across, while you hope to see a soundwave that only exists for a millionth of a second. Our hair-thin X-ray and optical laser beams had to meet on the mm-sized single-crystal diamond sample with a better timing accuracy than a nanosecond before the first data could be acquired. But we did it, and I believe these results will inspire a plethora of new research.”
The researchers demonstrated the imaging efficacy of a single X-ray pulse less than a thousandth of a nanosecond long. These findings open the door for visualizing stochastic and irreversible processes on a timescale of microseconds instead of the current milliseconds that are the common limit today.
“With this setup, we can investigate a wide range of ultrafast structural phenomena that have so far been beyond the reach of science. Visualizing structural processes on a timescale of less than a microsecond is relevant for solid-state physics, materials science, and geoscience. For example, when you want to understand processes in meta-materials, photonic crystals, thermoelectric materials, or even soft materials such as perylene and hybrid perovskites. Finally, it may be useful in geoscience to test seismological models of how sound travels in planetary materials,” said co-author Theodor S. Holstad.