Precise drilling with short pulsed lasers

Laser drilling is the oldest production technique using lasers. Nevertheless, the number of industrial applications is lying far behind of those of marking, cutting and welding. In cases when high accuracy is required, like for instance fuel injection nozzles, laser drilling could not fulfil the requirements, up to now. The major problem is the relatively large amount of molten material produced when using common drilling lasers with pulse durations in the order of one millisecond. Shortening the pulse length down to the femtosecond range is widely proposed as a recipe to avoid melt, now. The required laser systems, however, seem to need some years of ripening before they can be used in industrial environment. On the other hand, reliable and powerful diode pumped solid state lasers with pulse durations in the order of 10 nanoseconds are on the market now. Picosecond systems are available as laboratory setup. The paper presents drilling results obtained in both pulse regimes with fundamental and higher harmonic wavelengths. With a new drilling procedure, the so called helical drilling, an unprecedented level of accuracy could be achieved. A model allowing to explain experimental results will be offered.