LASER DRILLING OF ADVANCED MATERIALS - EFFECTS OF PEAK POWER, PULSE FORMAT, AND WAVELENGTH

The quality of laser-drilled holes is significantly influenced by the laser peak power, pulse format, and wavelength. Three advanced materia ls are used to demonstrate the importance of choosing the correct lase r parameters for a specific material. The materials are: (1) intermeta llic single crystal nickel aluminide (NiAl) alloy; (2) N5, a single cr ystal nickel-based superalloy; and (3) a silicon carbide (SiC) ceramic matrix composite (CMC). The Laser peak power is varied in terms of th e pulse duration and format. For low peak powers, long pulse format (p ulse lengths on the order of ms), conventional and also shaped-pulse ( burst) commercial rod Nd:YAG laser systems were used. For high peak po wers, a short pulse format was adopted for the laser used, namely a cw -pumped Q-switched or modelocked/Q-switched Nd:YAG oscillator followed by a cw-pumped multipass amplifier using a face-pumped, total interna l reflection Nd:YAG slab as the gain medium. Finally, a KrF excimer la ser operating at a 248 nm wavelength was used. The excimer wavelength was chosen to be close to the Nd:YAG fourth harmonic.