Brillouin-Interferometry: GFZ

Brillouin-Interferometry

Euler balance of the Brillouin system at GFZ Potsdam. The apparatus is designed for large experimental set-ups. — Euler balance of the Brillouin system at GFZ Potsdam *(Photo: R. Schulz, GFZ)*

Knowledge of the elastic properties of geomaterials at high P-T conditions plays a central role in determining the composition of the Earth's interior. The Brillouin interferometer at the Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences enables us to determine the sound wave velocities in minerals, glasses and liquids. For this purpose, we use so-called Brillouin scattering, i.e. the inelastic scattering of laser light by thermally activated lattice vibrations (phonons) in the analysed samples. Based on this data, it is possible to determine the total elasticity tensor, which determines the elastic response of a material under mechanical impact. This corresponds, for example, to the periodic distortion caused by the propagation of seismic waves in rocks.

Brillouin scattering laboratory in PETRA III

Left: spatial dispersion of acoustic velocity in a (110) plane of spinel (MgAl2O4) at high pressure in the diamond anvil cell (DAC). Center: a photo of the sample in the DAC. Right: X-ray diffraction photo of the sample in the DAC to determine its density at high pressure. *(Fig.: S. Speziale, GFZ)*

We have built, in collaboration with DESY HASYLAB, a new Brillouin spectroscopy system at PETRA III, the third generation synchrotron source in Hamburg. The new systems allows one to combine acoustic velocity measurements and density measurements by x-ray diffraction at the same experimental conditions at the extreme conditions beamline P02.2, next to the Brillouin scattering laboratory.