Pulsed Nd:YAG laser drilling of alumina ceramics and silicon wafers

This paper reports about drilling of alumina ceramics samples and silicon slabs with thickness about 2.3 mm, 7.5 mm and 8 mm using a stable and two types of non-stable resonator setups in pulsed Nd:YAG laser KLS 246-102 with different theoretical focus diameter and beam quality. Pulse energy and peak power were increased by setting of charging voltage from 280 V to 370 V with 10 V step for each type of resonator, their maximal values always depend on resonator power limits. Constant burst of pulses is applied on thinner samples to find holes dimensions dependence on peak power, than number of pulses needed to drill complete holes in thicker samples was investigated. Effect of the laser energy input and laser beam diameter on the holes depth and diameters was evaluated for all samples using both laser scanning confocal and optical stereo microscopes. It was observed, that achieved holes depth has tendency to increase with increasing value of the energy in case of blind holes, just as entrance/exit diameter of complete holes. Exit diameter of coneshaped holes is always smaller than that of the entrance. Maximal material removal was achieved with the most efficient stable resonator, but the best holes quality was obtain with non-stable resonator for drilling. Numerical model of the vaporized and melted area in the holes cross section was made using finite differences method to display temperature distribution dependence on increasing pulse energy.