  Time-domain Brillouin scattering technique, also known as picosecond
ultrasonic interferometry, which provides opportunity to monitor propagation of
nanometers to sub-micrometers length coherent acoustic pulses in the samples of
sub-micrometers to tens of micrometers dimensions, was applied to
depth-profiling of polycrystalline aggregate of ice compressed in a diamond
anvil cell to Megabar pressures. The technique allowed examination of
characteristic dimensions of elastic inhomogeneities and texturing of
polycrystalline ice in the direction normal to the diamond anvil surfaces with
sub-micrometer spatial resolution via time-resolved measurements of variations
in the propagation velocity of the acoustic pulse traveling in the compressed
sample. The achieved two-dimensional imaging of the polycrystalline ice
aggregate in-depth and in one of the lateral directions indicates the
feasibility of three-dimensional imaging and quantitative characterization of
acoustical, optical and acousto-optical properties of transparent
polycrystalline aggregates in diamond anvil cell with tens of nanometers
in-depth resolution and lateral spatial resolution controlled by pump laser
pulses focusing.
