Revealing Sub-$\mu$m and $\mu$m-Scale Textures in $H_2O$ Ice at Megabar Pressures by Time-Domain Brillouin Scattering

摘要

The time-domain Brillouin scattering technique, also known as picosecond ultrasonic interferometry,allows monitoring of the propagation of coherent acoustic pulses, having lengths ranging from nanometresto fractions of a micrometre, in samples with dimension of less than a micrometre to tens of micrometres. Inthis study, we applied this technique to depth-profiling of a polycrystalline aggregate of ice compressed in adiamond anvil cell to megabar pressures. The method allowed examination of the characteristic dimensionsof ice texturing in the direction normal to the diamond anvil surfaces with sub-micrometre spatialresolution via time-resolved measurements of the propagation velocity of the acoustic pulses travelling inthe compressed sample. The achieved imaging of ice in depth and in one of the lateral directions indicatesthe feasibility of three-dimensional imaging and quantitative characterisation of the acoustical, optical andacousto-optical properties of transparent polycrystalline aggregates in a diamond anvil cell with tens ofnanometres in-depth resolution and a lateral spatial resolution controlled by pump laser pulses focusing,which could approach hundreds of nanometres.