Laser Cleaning for Cultural Heritage

The use of pulsed laser radiation in order to remove extraneous materials from a solid substrate, i.e. the Laser Cleaning/Ablation (LC/LA) technique, in recent years has found an increasing interest in several fields ranging from microelectronics to cultural heritage. Within latter field the most common application is the removal of undesired surface layers (e.g. fungi, bacteria, pollution crusts, corrosion layers, surface treatments, etc.) from artifacts of both inorganic (stones, metals, glasses, etc.) and organic (wood, paper, parchment, textiles, etc.) materials. In order to achieve good results the operating parameters (i.e. laser beam wavelength, fluence, pulse repetition rate, etc.) must be set to avoid damaging the substrate to be preserved and to efficiently remove undesired material. Therefore a correct application of the LC/LA technique requires a good knowledge of the effects of laser radiation interaction with both the substance to be removed and the substrate. A lot of experimental work has been carried out and several papers have been written describing several more or less general techniques and some specific applications. The aim of the present work is to summarize and present in an organic manner the LC/LA techniques applied to cultural heritage from both a theoretical and an application point of view. In the first section we briefly describe the main (Laser Ablation, Dry Laser Cleaning, Steam Laser Cleaning) and some other specific (Angular Laser Cleaning, Laser Induced Buckling/Detaching, Laser Shock Cleaning, Verso Laser Cleaning) techniques. In the second section we first summarize the basic physical problems (laser heating, thermo-elastic wave generation, particle - surface adhesion/removal) whose knowledge is required to fully understand the LC/LA. After that we present some models for the description of main LC/LA techniques. Third section is devoted to a review of LC/LA applications in the field of cultural heritage with the aim to collect and summarize the large amount of experimental work carried out in recent years.