Spectroscopic diagnostics of plasma during laser processing

The role of the plasma in laser–metal interaction is of considerable interest due to its influence in the energy transfer mechanism in industrial laser materials processing. A 10 kW CO2 laser was used to study its interaction with aluminium under an argon environment. The objective was to determine the absorption and refraction of the laser beam through the plasma during the processing of aluminium. Laser processing of aluminium is becoming an important topic for many industries, including the automobile industry. The spectroscopic relative line to continuum method was used to determine the electron temperature distribution within the plasma by investigating the 4158 Å Ar I line emission and the continuum adjacent to it. The plasmas are induced in 1.0 atm pure Ar environment over a translating Al target, using f/7 and 10 kW CO2 laser. Spectroscopic data indicated that the plasma composition and behaviour were Ar-dominated. Experimental results indicated the plasma core temperature to be 14 000–15 300 K over the incident range of laser powers investigated from 5 to 7 kW. It was found that 7.5–29% of the incident laser power was absorbed by the plasma. Cross-section analysis of the melt pools from the Al samples revealed the absence of any key-hole formation and confirmed that the energy transfer mechanism in the targets was conduction dominated for the reported range of experimental data.