Plume Heat Transfer in Laser Processing of Materials

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This study is an investigation of the mechanisms of heat transfer associated with plume formation occurring during the interaction of laser radiation with metal targets. The primary objective of the study is the development of techniques which can be used to determine the relative importance of plume absorption, scattering, and emission on coupling of laser energy into metal targets. The methods used include high speed photography, target temperature measurement, plume light scattering and transmission measurements, and calibrated plume emission spectroscopy. A pulsed Nd-YAG laser is used as the primary source of incident laser radiation at flux levels of 105 W/cm2 and greater. Aluminum and aluminum alloy materials are used as targets. Another objective of this study is the investigation of the role of the assist gas on plume ionization and coupling of laser energy into the workpiece. The influence of molecular oxygen on degree of plume ionization is studied by performing tests in various atmospheres with and without molecular oxygen. The significance of this study is that a clearer understanding of the heat transfer mechanisms associated with plume formation is expected to be obtained. This study will help accomplish the long term goal of this research program which is to provide an understanding of heat transfer mechanisms in laser target interaction so that lasers may be utilized to their full advantage in materials processing.