Plume Heat Transfer in Laser Processing of Materials

本文研究了激光与金属靶相互作用过程中与羽流形成有关的换热机理。这项研究的主要目标是开发可用于确定羽流吸收、散射和发射对激光能量耦合到金属目标的相对重要性的技术。使用的方法包括高速摄影、目标温度测量、羽流光散射和透射率测量以及校准的羽流发射光谱。脉冲激光作为入射激光的主要光源，通量水平为105W/cm2或更高。使用铝和铝合金材料作为靶标。这项研究的另一个目的是研究辅助气体在羽流电离和激光能量耦合到工件中的作用。通过在不同大气中有无分子氧的实验，研究了分子氧对羽流电离度的影响。这项研究的意义在于，人们有望更清楚地了解与羽流形成相关的热传递机制。这项研究将有助于实现这一研究计划的长期目标，即了解激光与靶相互作用的热传导机制，以便充分利用激光在材料加工中的优势。

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.