FUNDAMENTAL INVESTIGATIONS OF MICROMACHINING BY NANOSECOND AND PICOSECOND LASER-RADIATION

The removal processes of ceramics and metals were investigated using p ico-and nanosecond laser radiation produced by diode-pumped Nd:YAG las ers. The laser radiation was focused to spot diameters smaller than 10 mu m, yielding power densities up to 5 X 10(12) W/cm(2). The threshol d fluence for removal and the removal depth per pulse were determined for 40 pico- and 10 nanosecond laser pulses using the fundamental wave length, the second harmonic and the third harmonic laser radiation of the laser system. For 40 ps laser pulses pump and probe investigations were used to study the interaction of intense ultrashort laser beams with matter. By this technique ultrashort processes can be photographe d with a time resolution determined by the pulse length of pump and pr obe pulses. The measurements allow a detailed characterization of the material removal including melting, vaporization and fast resolidifica tion as well as the feedback of the surrounding atmosphere to the proc essed microstructures. The threshold fluences for material removal and the removal rates per pulse were determined for Si3N4, SiC and WC as a function of laser pulse length and laser wavelength. Using picosecon d laser radiation microstructures were produced in different ceramics and metals demonstrating the suitability of short laser pulses for the production of microstructures with dimensions smaller than 10 mu m an d for ultra-precise removal of thin layers. (C) 1998 Elsevier Science B.V.