雷射應用於文化資產清潔之臨界能量研究

A study on the threshold fluence of laser application in the cleaning of cultural heritage

一般文物與古蹟建築體表面容易受到各式汙染，造成外觀劣化、損壞或被汙染物覆蓋原貌等問題，所以透過對受到汙染的文物進行清潔，可以提升文化資產的美學價值，亦可避免汙染物對文物造成損壞。然而，常用的機械力清潔法與化學藥劑清潔法，均可能導致重要文物的損壞或造成材質汙染，另外一方面，雷射因能量不具累積性，因此不易造成文物後續的傷害，故雷射清潔在國際上是進行重要文物的清潔方法之一。而在各種雷射中，目前以Nd:YAG雷射（釹釔鋁石榴石雷射，波長：1064nm）最常應用於文物清潔作業，因此本研究以Nd:YAG雷射為研究對象，探討各種材質（金屬、石材、陶瓷、木材及彩繪）在乾式及濕式清潔條件下所能承受Nd:YAG雷射之臨界能量密度。研究結果顯示，在各種研究材料中以彩繪類試片所能承受之臨界能量密度最低，而石材與木材類試片所能承受之臨界能量密度則相對較高。

The exteriors of cultural heritage objects (including antiquities) and historic buildings are readily contaminated by various pollutants. These surface pollutants not only hide the original colors and decorative surface details, but also have the chance to damage the substrates of the heritage. Cleaning the soiled surfaces will not only increase the aesthetic value of cultural heritage but also reduce potential future deterioration. Unfortunately, the traditional physical and chemical cleaning methods commonly used could damage or further pollute the substrate of the historical objects that we want to protect, even in careful operation. Compared with traditional methods, laser cleaning is less aggressive and more controllable because it leaves no residues and the cleaning action stops immediately as the laser power is shut down. Hence the interest shown recently in using laser cleaning as a technique for some important classes of cultural heritage. There are many kinds of laser but Nd:YAG (neodymiumdoped yttrium aluminum garnet; wave length 1064nm) laser is one of the most commonly used in the heritage conservation field. Accordingly, this study focuses on the application of Nd:YAG lasers and the tolerance of various materials (metal, stone, pottery, wood, and painting) under conditions of dry cleaning and wet cleaning to the ablation threshold of Nd:YAG laser. The results indicate that, among the materials studied, the paint specimens had the lowest tolerance in terms of ablation threshold, whereas the stone and wood specimens tolerated comparatively high ablation threshold.