Measurement of plasma plume in laser welding by IR radiation

In this paper, a new method of plasma diagnostics, where infrared (IR) radiation from a plasma is detected for measuring the electron density of the plasma, has been applied to analyze the plasma property of laser plume in CO2 laser welding. The system of CCD camera and IR filter, proposed in this work, makes it possible to derive an instantaneous electron density profile of laser plume during welding from its CCD image.As a result of the measurement under various process conditions, it is made clear that the laser plume is a high density plasma, and the peak electron density, changing violently, is higher than 1023[m 3] and it is high enough for laser plume to absorb partially CO2 laser beam power.