Effects of laser beam spatial distribution on laser-material interaction

The efficiency of any laser materials processing depends on the efficient energy transfer from the laser to a substrate. One of the critical factors in the process is the spatial distribution or the “mode” of the laser beam. Although an inverse Bremsstrahlung initiates the photon to electron energy transfer, a major part of the process is transport phenomena created by the absorbed energy. A mathematical model for transport phenomena during laser materials interaction is developed that includes multiple reflections, capillary and thermocapillary forces, recoil pressure, temperature distribution, melt pool flow, and phase changes. This model simulates interaction between a CO2 laser (λ = 10.6 μm) with four different spatial distributions and iron. The results of a simulation for fundamental understanding of this laser-material interaction are presented in this paper. First, overall keyhole behaviors are compared in terms of response time, penetration hole geometry, and absorptivity. Furthermore, a dimensionless parameter is developed to examine keyhole collapse quantitatively. Finally, velocity, temperature, and, intensity fields are analyzed.