Monitoring of Laser Materials Processing

在等离子体连续辐射理论的基础上，提出了一种新的等离子体诊断方法--红外等离子体诊断法，并阐明了这种方法对高密度低温等离子体（如电弧等离子体）电子密度的测量是有用的。用该方法精确地讨论了氩保护气体钨极电弧的电子密度分布，明确了大电流氩保护气体钨极电弧的电子密度分布在阴极附近区域有一个离轴峰，与氩等离子体的电子密度峰值相对应，在第二部分中，我们将诊断方法应用于CO_2激光焊接中激光诱导等离子体的特性分析。结果表明，CO_2激光诱导的等离子体是一种高密度等离子体，其峰值密度大于10^<23>[m^<-3>]，足以使激光羽吸收部分CO_2激光功率，从而说明红外光谱法为激光等离子体诊断和激光工艺监测提供了一种简单而有效的手段。

A new method of plasma diagnostics, based on the continuous radiation theory of plasma, has been proposed in the previous papers, and it has been clarified that the method, called "IR plasma diagnostics method", is useful for the measurement of electron density of high density and low temperature plasma, such as arc plasma.In the first part of this study, the electron density profile of Ar-shielded gas tungsten arc has been discussed precisely by using the method, and it is made clear that the density profile of high current Ar-shielded GTA has an off-axis peak in the zone near cathode, which corresponds to the peak electron density of Ar-plasma, expected at 17000K under thermal equilibrium condition.In the second part, the diagnostic method has been applied to analyze the property of laser induced plasma in CO_2 laser welding. It is clarified that the plasma induced by CO_2 laser beam is a high density plasma and its peak density is higher than 10^<23> [m^<-3>], and the density is high enough for laser plume to absorb partially CO_2 laser beam power.Accordingly, it is concluded that the IR method offers a simple and powerful means of laser plasma diagnostics and laser process monitoring.