Laser processing analysis and research: tracking code 94-ERP-071. Final report

This Exploratory Research Project addressed the coupling between short pulse, short wave length, high-radiance laser beams and a solid substrate. The motivation for conducting this research stems from the ever increasing application of high-radiance lasers in processing materials for science and industry. As a result of extensive research and development activities at Lawrence Livermore National Laboratory, there are now several lasers that can cut metals, ceramics, and composites rapidly with unmatched precision. Both gas and solid state lasers are now being employed in this area. The purpose of this project is to develop scientific understanding of the cutting process and to provide tools to optimize the laser system for various applications like precision hole drilling, cutting, welding, and ablative coating. There is a significant amount of scientific data and model development that supports this area of study. Kar and Mazumder reported on studies of pulsed laser coupling for the creation of nano-particles. This provided the initial motivation for our model. Here we include a more detailed discussion of light absorption and propagation, and electron plasma effects and expansion into an ambient gas rather than only in a vacuum. Our first effort began in FY1994, which yielded the basic model. In FY1995, we refined the code and later identified a more appropriate equation of state. The experimental program and the modeling effort provided the essential parametric evaluations needed to benchmark the model. This program enabled us to discover several underlying plasma effects important to the cutting or ablation process. Extensive measurements of the plume of expanding vapor and optical emissions give plasma temperatures, densities, and hydrodynamic estimates of the vapor`s neutral properties. In the first studies, both aluminum and iron are treated. Carbon studies were included in the final phases of this work. 3 refs