Measurements of Dynamic Structural Changes in Laser‐Shocked Materials by Positron Annihilation

Standard shock wave measurements provide no information about the structural changes in the lattice during the generation and propagation of shock waves. It is important to acquire such information to understand the mechanisms of defect formation in laser processing of materials. Positron annihilation spectroscopy has been shown to be a valuable tool to study electron states and open volume defects in solids for more than 40 years. We report the first dynamic measurements of positron annihilation during short‐pulsed laser irradiation of materials. Nanosecond high‐power laser pulses were synchronized with nanosecond bremsstrahlung pulses from a 30 MeV electron linac to irradiate the materials. Bremsstrahlung photons generate positrons inside the material. These positrons, in turn, annihilate with the shocked material’s electrons emitting 511 keV radiation, which is influenced by the momentum distributions of the electrons. Due to positron trapping at defects, structural changes of the lattice are reflected...