Plume Heat Transfer in Laser Processing of Materials

本文研究了激光辐射与金属靶相互作用过程中与羽流形成相关的传热机制。本研究的主要目的是发展技术，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。使用的方法包括高速摄影、目标温度测量、羽流光散射和透射测量以及校准羽流发射光谱。脉冲Nd-YAG激光器被用作入射激光辐射的主要来源，其通量水平为105w /cm2或更大。铝及铝合金材料作为靶材。本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。通过在有和无分子氧的不同气氛下进行试验，研究了分子氧对烟羽电离度的影响。本研究的意义在于对与羽流形成相关的传热机制有了更清晰的认识。这项研究将有助于实现本研究计划的长期目标，即提供对激光靶相互作用中的传热机制的理解，以便激光可以在材料加工中充分发挥其优势。

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.