Laser penetration of metal targets with high powers of up to 120 kW

Since high-power fiber lasers are emerging in the field of directed energy, the fundamental interaction of these lasers with target materials has to be investigated. For this purpose, experiments with short propagation distances can be performed. The aspects of high-power propagation through the atmosphere over large distances are excluded and go beyond the scope of this work. We show experimental results of laser-matter interaction with up to 120kW continuous wave laser power. The targets are 10mm thick plates of aluminum and steel as representative materials commonly used for construction purposes. A decreasing perforation time is observed with increasing laser power. For low powers, the aluminum samples show a much higher perforation time compared to the steel samples. This changes at roughly 80 kW. Above this value the steel samples withstand the laser irradiation longer. This behavior can be attributed to the much higher thermal conductivity of aluminum compared to steel. The change of dominant effects from low to high laser powers is discussed. One further important aspect is the effective energy coupling into the sample. This is investigated by finite element simulations with an adjustable absorptivity. For the steel samples a high absorption rate of around 75% is observed at low laser powers, which drops down to roughly 15% at the highest laser powers. For the aluminum samples, on the other hand, an almost constant value of around 15% is observed.