Fundamental investigations of micromachining by nano- and picosecond laser radiation

The removal processes of ceramics and metals were investigated using pico- and nanosecond laser radiation produced by diode-pumped Nd:YAG lasers. The laser radiation was focused to spot diameters smaller than 10 mm, yielding power densities up to 5 = 10 12 Wrcm 2 . The threshold fluence for removal and the removal depth per pulse were determined for 40 pico- and 10 nanosecond laser pulses using the fundamental wavelength, 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 photographed with a time resolution determined by the pulse length of pump and probe pulses. The measurements allow a detailed characterization of the material removal including melting, vaporization and fast resolidification as well as the feedback of the surrounding atmosphere to the processed microstructures. The threshold fluences for material removal and the removal rates per pulse were determined for Si N , SiC and WC as a function of laser pulse length and laser wavelength. Using picosecond laser 34 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 mm and for ultra-precise removal of thin layers. q 1998 Elsevier Science B.V.