Micro-holes of 100 to 300μm diameters have been drilled on plates of cemented tungsten carbide of 0.5 to 1 mm thick using ultrashort laser pulses. Laser was scanned by a galvano-scanner with scan speed of 0.035 to 15 mm/s and focused by lens with 80 mm focal length. Effects of scan speed, focus position and polarization of the laser, linear vs. circular, were examined. It is found that the polarization of the laser has profound effects on the shape of the drilled hole: circularly polarized laser results in more straight, less tapered holes than the linearly polarized one in shorter times. Position of the focus relative to the sample surface affects to the hole shape, too. Periodic surface structures with 260 to 300 nm periods are formed on the side of drilled holes regardless the polarization of the laser.
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