The plasma plume expansion process of an AIN target ablated by an ultra-short Nd:glass pulsed laser (200 fs, 1.2 ps) has been surveyed by emission spectroscopy and fast imaging. The data have been collected with spatial and temporal resolution in order to find out the species speed and their angular distribution. Furthermore, it has been possible to discriminate different regimes involved during the plasma expansion by comparing the data so obtained with previous studies performed with ns laser sources. These results could also justify the cluster formation, detected by a quadrupole m ass spectrometer, observed during the ultra-short laser ablation regime, but not for the ns one. (C) 2002 Elsevier Science B.V. All rights reserved.