Laser cleaning of alumina particles on glass and silica substrates: Experiment and quasistatic model

Abstract

Silica and microscope slides that had been pretreated with a variety of wet chemical, ultrasonic and laser irradiation surface preparation methods were contaminated with alumina particles of around 3 μm. The samples were prepared and processed without delay so as to avoid capillary condensation in a high humidity environment and thus ensuring that the process is dry laser cleaning. They were then irradiated with a pulse of 248 nm radiation from a KrF excimer laser, over a range of fluences. The laser cleaning results show that, in this case, the surface preparation method appears to have little effect on the laser cleaning efficiency. They also demonstrate that the threshold fluence for particle removal of silica is approximately eight times higher than that for microscope slides, when so prepared. In contrast, application of Arnold et al.’s thermal expansion model of laser cleaning in the quasistatic limit to this material system predicts that the threshold fluence for silica will be about 15 times greater than that for glass. One possible explanation for this discrepancy may be that the particle’s absorptivity (0.16) is inaccurate. A value of 0.35 gives good agreement between theory and experiment.