Filming phonons

This 3D shape is actually a still from a billion-frames-a-second film made at University College London, UK. There, Jesse Clark’s team has been working on 3D imaging of gold nanocrystals. The latest work involved hitting the nanocrystals a laser pulse of infra red light to set the nanocrystal vibrating, before taking snapshots of the vibrations with femtosecond X-ray pulses. Because the X-ray pulses are so short the atoms in the nanocrystal are effectively static. By taking multiple images the team can see how the light causes vibrations in the nanocrystal - here blue shows areas of contraction while red shows areas of expansion.

The team found that the vibrations start at the same moment everywhere in the crystal rather than starting in one area and propogating through the structure as you might expect. Studying the phonons (vibrating atoms) can help improve and validate molecular dynamics simulations.