The applicability of the Sedov-Taylor scaling during material removal of metals and oxide layers with pulsed CO2 and excimer laser radiation

For the removal of material with pulsed laser radiation the distance travelled by the shock or blast wave and the amount of energy released in the plasma state due to the absorption of laser radiation are determined experimentally and theoretically. The distance travelled by the blast wave is detected by schlieren photography, the released energy by monitoring the transmitted laser radiation during the removal process. The theoretical evaluation is performed by numerical simulation using a model incorporating the laser-induced vaporization process and the dynamics of the plasma state. The results obtained from the experiments and the model are compared with that of the Sedov-Taylor scaling. The removal of the oxide layer from austenitic steel is investigated with CO2 laser radiation produced by a TEA and a high-power CO2 laser device. For the TEA laser with fluences of 5 and 10 J cm(-2) 50-80% of the pulse energy is released into the plasma state and the Sedov-Taylor scaling describes the distance travelled by the blast wave in agreement with data from the experiments and the simulation. For the high-power CO2 laser with a fluence of 50 J cm(-2), 6% of the pulse energy is released into the plasma state and the Sedov-Taylor scaling does not describe the data of the simulation. The process of removal of copper and aluminium material is simulated for excimer laser radiation with fluences of 15 and 30 J cm(-2). For copper 15-30% of the pulse energy is released into the plasma state and the Sedov-Taylor scaling is applicable. For aluminium, less than 2% of the pulse energy is released into the plasma state and the Sedov-Taylor scaling is only applicable for the higher fluence.