Detailed studies of the plume deflection effect during sub-ps laser ablation of Si target

For the first time the plume deflection effect during the irradiation of silicon target with sub-ps KrF laser pulses was investigated. The morphological changes of the laser ablated target and the corresponding plume deflection angle have been studied in vacuum with different laser fluences and number of pulses. In accordance with earlier results obtained by nanosecond laser, we found a strong correlation between the morphological changes on the irradiated target and the observed plume deflection angle. As the number of laser pulses increases, the formation of well-defined silicon columnar microstructures oriented towards the laser beam has been observed on the targets ablated with fluences between 0.1 and 1.7 J/cm2 (2.2 × 1011 and 37.4 × 1011 W/cm2 of power density, respectively). It has also been observed that the plume deflection effect is present for laser fluences between 0.1 and 1.2 J/cm2, with a maximum deflection angle always higher than 20°. Simultaneously, an array of silicon substrates placed on a hemi-cylindrical holder was used for deposition experiments, in order to study the influence of the plume deflection on the thickness distribution profile of the deposited films. Profilometric analyses of the deposited silicon films revealed a non-uniform material deposition. Comparison with the results obtained by nanosecond lasers is reported and discussed.