Ultrafast lasers for conservation of heritage artefacts

Abstract

The use of laser technology for cleaning heritage artefacts is gaining increasing interest both in Australia and overseas. Laser cleaning is a dry and contact-free process, which selectively removes contaminating dirt or coatings (including hazardous contaminants such as radioactivity and biological material), minimises mechanical and chemical disruption of historic surfaces and generates minimal waste. However, the disadvantage of current lasers for conservation is that their relatively long pulse duration allows heat and shock waves to travel into the substrate, potentially causing damage to historic surfaces. Different laser types are also needed to treat different materials, which limits the range of materials any one laser unit can treat. The femtosecond pulses used by ultrafast lasers however, are too short to allow heat or shock waves to travel into the substrate. They ablate very thin surface layers through a process known as non-thermal or non-equilibrium laser ablation. This allows highly controlled cleaning, does not affect the substrate material, and can be combined with real-time monitoring with a system such as Laser-Induced Breakdown Spectroscopy to analyse the ablated products and prevent damage to uncontaminated layers under the surface of an object. This paper describes the differences between conventional and ultrafast lasers, and outlines the aims of a new Australia Research Council project to develop the ultrafast laser technique for conservation