Experimental investigation of ablation mechanisms involved in dry laser cleaning

The various ablation mechanisms possibly involved in ‘laser-particle-surface’ interaction were investigated by means of in situ diagnostics. Different kind of transparent and absorbing particles were irradiated by UV nanosecond laser pulses. Optical microscopy was employed to measure particle removal efficiencies and fluence thresholds. Fast imaging with the aid of an intensified charged coupled device (ICCD) camera was used to characterize the ejection of species on a microsecond time scale. The present study shows that laser irradiation of particles can induce the damage of surfaces as a result of near-field enhancement underneath particles and/or thermal contact with hot particles. During the experiments of laser ablation of contaminants made of carbon-based materials, the contribution of the photochemical degradation was evaluated. The photochemical ablation mechanism is of great interest for the removal of contaminates at low laser fluence. The results of this study are discussed in terms of admissible mechanisms which lead to particle removal in dry laser cleaning experiments with nanosecond laser pulses.