Accumulation effects in laser ablation of metals with high-repetition-rate lasers

Abstract

Effects related to the use of high repetition rate lasers in ablation of metals (aluminum, copper, stainless steel) and silicon were investigated. The multi-pulse irradiation with the laser beam significantly lowered the ablation threshold and led to a relative increase in the ablation rate at the higher repetition rate. The reason of alteration could be accumulation of structural defects on the metal surface formed by irradiation with a laser of the sub-threshold fluence. The mean volumetric ablation rate in laser milling experiments was a non-linear function of the pulse energy. Plasma shielding was the main limiting factor in processing efficiency of metals with the high power picosecond lasers. Increasing the repetition rate keeping the pulse energy below the plasma formation threshold is a way to increase the efficiency of material removal with nanosecond lasers. Thermal management of the specimen could be a problem at high repetition rates because of the laser energy wasted in the bulk. The reduction in the ablation threshold by irradiation with a series of laser pulses might be useful in application of the high- repetition-rate lasers with the low pulse energy.