Removal of silica microspheres from glass and silica substrates by dry laser cleaning

Laser cleaning of 5.0 µm diameter silica spheres from silica surfaces was investigated. It was found that for three different slide preparation methods that the particles did not adhere strongly to the silica substrate. Experimental laser cleaning particle removal thresholds were 4 orders of magnitude less than that predicted by theoretical modelling based on thermal expansion and Van der Waals adhesion. There are two reasons put forward to explain this discrepancy. The first is that there are other forces acting on the particle besides the Van der Waals force. This is supported both by the present study which found that silica spheres did not adhere strongly to silica slides for three different preparation methods and by previous atomic force microscope (AFM) and surface force apparatus (SF A) studies which showed the existence of a short range repulsive force between silica spheres and silica substrates. The second explanation is that the spheres have a greater effective absorption coefficient than that of bulk silica. This was supported by the fact that at high fluences small hillocks of silica remained after irradiation indicating that temperatures in excess of 1900 K had been achieved. Both factors taken together can account for the discrepancy between theoretical predictions and experimental results in the present study.