A study on fresnel absorption and reflections in the keyhole in deep penetration laser welding

On the basis of a keyhole photograph obtained experimentally, the keyhole profiles are determined by the method of polynomial fitting. Then the behaviour of the laser beam in the keyhole is analysed by tracing a ray of light using geometrical optics theory; the Fresnel absorption and reflections in the keyhole are systematically studied, and the laser intensities absorbed on the keyhole walls are calculated. By comparing the laser Intensity absorbed on the keyhole walls with the heat flux lost there, the mechanism of energy balance on the keyhole walls is discussed.