Mechanisms of ultra-fast laser ablation during deep-drilling of metals was studied using plasma diagnostics and morphological analyses of the laser-induced craters. Fast imaging and time- and space-resolved optical emission spectroscopy were employed to characterize the ablation plume. After irradiation, the crater morphology was analyzed by scanning electron microscopy and optical microscopy. From the correlation between the ablation plume characteristics and the shape of the laser-produced craters. it is shown that the nanoparticles have an important influence on the accuracy of rnicromachining by ultra-short laser pulses. (c) 2005 Elsevier B.V. All rights reserved.