Laser Pulse Heating and Vapor Front Generation

Laser nonconduction limited heating situation results in cavity formation and vapor front development above the cavity. As laser heating progresses, cavity wall recesses towards the solid bulk while the vapor front expands into its ambient due to recoil pressure generated at liquid-vapor interface in the cavity. To obtain velocity, temperature, and pressure fields in the evaporating front become challenging, since the process involves with transient evaporation of the surface during the absorption of the laser energy by the solid substrate. In the present study, phase change processes taking place in the substrate material during a laser heating process are modeled using an energy method and evaporating front behavior is modeled using the transient flow equations. Since the problem is involved with the multi-physics, the numerical technique is introduced to solve the resulting governing equations. The water ambient is assumed around the cavity in order to resemble the laser processing situation, particularly for laser shock processing. It is found that for nanosecond pulses with high intensity, the recession velocity of the surface reaches about 100 m/s at the symmetry axis and the recoil pressure of in the order of 10 GPa is generated in the cavity as a result of rapid evaporation. © 2008 American Institute of Chemical Engineers AIChE J, 2008