ABSTRACT

In addition to the thermal expansion of the substrate the early publications on laser cleaning [6, 7, 9, 10] suggested a second mechanism for the removal of dirt particles: the explosive evaporation of a liquid such as water or alcohol. Here the liquid layer is heated directly [10] (laser energy absorbed in the liquid) or indirectly [6, 7] (laser energy absorbed in the substrate and transferred to the liquid via heat conduction) by the laser pulse. Due to the short time scale of this heating the liquid is superheated to a certain extent, becomes intrinsically unstable and subsequently evaporates explosively. The momentum transfer of this explosion onto the particle is then thought to lift the particles off the surface. In the following, we will discuss this cleaning mechanism in three variations: the evaporation of liquid adsorbed at the particle-surface area as it is the case for DLC in ambient air, the evaporation of a liquid film as it is found in SLC, and the laser induced nucleation of bubbles in a bulk liquid that provides considerable information on the underlying physics.