The PI will assemble a laboratory at the University of Washington for the purpose of measuring sound velocities of candidate mantle minerals at high pressure and temperature. On the basis of successful preliminary experiments, he has demonstrated that it is feasible to make such measurements on small (100 um) samples in a diamond anvil high pressure cell. Impulsive stimulated scattering (ISS) in the form of laser induced phonon spectroscopy provides a robust technique to investigate the elastic properties of crystals at high pressure. Coherent phonons, generated by a pair of overlapping laser pulses, temporally and spatially modulate the index of refraction of sample. A probe laser pulse can be strongly diffracted by the resultant time-dependent grating. Signals are orders of magnitude greater than with any other technique. This technique also side-steps the uncertain index-of-refraction problem often associated with Brillouin scattering experiments. The determination, under mantle conditions, of pressure and temperature derivatives of elastic constants for candidate mantle constituents is one of the important current problems in mineral physics.
