Mechanisms of laser cleaning

Laser cleaning is growing in importance with the introduction of the Montreal protocol which proposes the long term reduction on environmental and public health grounds in the use of organic solvents such as CFCs that are normally used in industrial cleaning. There is also significant interest in laser cleaning in the conservation of sculptures, paintings and museum objects where the process offers advantages in terms of time saving and the enhancement of the ability to conserve certain artefacts. To date there has been insufficient consideration of the mechanisms involved in laser cleaning and how their understanding could lead to improved control and efficiency of the laser cleaning process. This paper considers an overview of the processes involved and their relevance in the different cleaning situations encountered in practice, mainly in terms of the application short pulse length lasers. The mechanisms to be considered include, (1) photon pressure, (2) selective vaporization, (3) shock waves produced by rapid heating and cooling, (4) evaporation pressure, (5) plasma detonation (spallation), (6) ablation.