Absorption of laser energy by a welding arc

In laser/arc hybrid welding system a unitary heat source is built by combining a laser beam with an electric arc. In this combined heat source, the laser beam has to pass through the high temperature, highly ionised arc plasma before it can reach the workpiece to be welded. The objective of the study is to determine how much of the laser energy is absorbed by a welding arc since arc plasma is not fully transparent to Nd:YAG laser beam. Experimental measurements were conducted by making use of a laser power meter. Readings from the meter were compared with and without the laser beam passing through an electric arc under various conditions. The absorption coefficient was calculated using a simple exponential relationship. Experiments were specifically designed to evaluate two groups of influencing factors on the absorption coefficient. Varying the welding arc current from 50 to 250 A and using shielding gases of pure argon, pure helium and helium with metal vapour enabled the evaluation of different the plasma states for laser powers of 500W and 3 kW.