Percussion drilling with high power Nd:YAG lasers

The increase of efficiency of gas turbine components asks for improved cooling by a large number of film cooling holes. Laser percussion drilling is the most cost-effective process to produce these holes. A simplified model is introduced. It gives the dependence of the hole diameter on pulse energy, pulse length, beam quality and focus position. Experimental results of three lasers with different design of optical resonator are compared. It is demonstrated that the ring resonator gives the best beam quality. Burn patterns are normally used to asses the beam profile. A double burn pattern method is introduced. Furthermore it is demonstrated that CCD based beam analyzers are best suited for beam quality monitoring.