Picosecond Acoustics: a Laser Pump-Probe Technique for the Determination of Thermo-Elastic Properties of Solids and Liquids at High Pressure and High Temperature

Abstract:

Picosecond acoustics is a time-resolved optical pump-probe technique that allows studying the propagation of acoustic waves in a large variety of samples, be these crystalline or amorphous solids, liquids, opaque or transparent, metallic or insulating. In addition to time of flight measurements, analogous in many aspects to the classical ultrasonic pulse-echo technique, it can provide phonon surface imaging as a function of time, or time-resolved stimulated Brillouin scattering.

Here we present an experimental setup combining picosecond acoustics with diamond anvil cell, resistive heating and laser heating, which can be used for laboratory determination over an extended pressure and temperature range of: (i) melting curves and phase diagrams; (ii) the complete set of elastic moduli for single crystals; (iii) longitudinal velocities for polycrystalline samples; and (iv) adiabatic velocities, thermo-elastic properties and equation of state for liquids.

To illustrate the capabilities of the technique, examples of studies of direct interest to Earth and planetary science will be provided, including measurements on iron and iron alloys, metallic liquids, hydrogen and deuterium, and ongoing work on cubic oxides (MgO and Fe₃O₄).