Simulation of laser-generated longitudinal and shear ultrasonic waves in a diamond anvil cell by the finite element method

Based on the thermoelastic theory, a numerical model of ultrasonic displacement field induced by a vertical incident pulsed laser in an aluminum film in a diamond anvil cell (DAC) is established by using the finite element method (FEM). After precisely calculating the transient temperature field distributions, the bulk ultrasonic waveforms on the rear surface of the film and the characteristics of ultrasonic displacement field with time are obtained. Then directivity patterns of laser-generated longitudinal and shear ultrasonic waves are analyzed in details. The numerical results indicate that the thermoelastic force source and the characteristics of ultrasonic directivity are strongly affected by the diamond window. The energy of longitudinal wave is concentrated near the laser incident direction, and the one of shear wave is concentrated between 30 degrees and 60 degrees that deflected from the laser incident direction to the excited source. These characteristics in DAC system are different from the results of free surface in thermoelastic effect, while are similar to the results of free surface in ablation effect. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676253]