We study the formation mechanism of rims created around femtosecond laser ablated craters on glass. Experimental studies of the surface morphology reveal that a thin rim is formed around the smooth craters and is raised above the undamaged surface by about 50-100 nm. To investigate the mechanism of rim formation following a single ultrafast laser pulse, we perform a one-dimensional theoretical analysis of the thermal and fluid processes involved in the ablation process. The results indicate the existence of a very thin melted zone below the surface and suggest that the rim is formed by the high pressure plasma producing a pressure-driven fluid motion of the molten material outwards from the centre of the crater. The numerical solutions of pressure-driven fluid motion of the thin melt demonstrate that the melt can flow to the crater edge and form a rim within the first nanoseconds of the ablation process. The possibility that a tall rim can be formed during the initial stages of the plasma is suggestive that the rim may tilt outwards towards the low pressure region creating a resolidified melt splash as observed in the experiments. The possibility of controlling or suppressing the rim formation is discussed also.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Acoustics and Ultrasonics
- Surfaces, Coatings and Films