Equivalent power densities model for multi-pulse ultrashort pulsed laser processing

Ultrashort pulsed laser, due to its extremely high peak power density, has been widely used for high precision, rapid and programmable manufacture. Several models, such as two-temperature model (TTM) and a molecular dynamics model, have been proposed for the temperature simulation or clarifying the nonequilibrium phase transition. However, there exists no an appropriate theory guiding for effective selection of laser parameters. Here, an equivalent power density (EPD) model was proposed to describe the morphological evolution of the phase transition area and guide for proper laser parameters selection. Based on EPD model, theoretical analysis was carried out for laser cutting, laser processing in transparent materials, and the formation of laser induced periodic surface structures (LIPSS), and it was verified that material phase transition can be determined by both the laser power density and the temperature field. Through the three kinds of laser processing experiments, including laser cutting, laser dotting and scanning as well as laser welding glass, it was demonstrated that the experimental results can be well explained by the EPD model.