Generation of particles and fragments by quasicontinuous wave fiber laser irradiation of stainless steel, alumina, and concrete materials

An experimental characterization is presented on fine particles, droplets, and fragments produced at the interaction region between a 2.7 kW quasicontinuous wave (repetitive pulsed operation with a 10 ms pulse duration) fiber laser and stainless steel, alumina, and heavy concrete samples. In the samples, the recoil pressure induced by vaporization pushes particles and fragments into the ambient atmosphere. In order to preserve a safe working environment, in particular for nuclear decommissioning, special care should be taken to confine and retrieve such particles during laser processing. In the experiments, particle production from the vapor and the molten phase layer in the targeted material was observed with a high-speed camera, with fine particles collected and analyzed using an electron microscope. The observed results were qualitatively interpreted with the help of a simplified one-dimensional hydrodynamic code coupled with a stress computation code. Characterization and classification of the results are expected to provide a useful database that will contribute to the decommissioning of nuclear facilities and other industrial applications.