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Researchers have shown that lasers can be used successfully as a non-destructive technique for analyzing and identifying materials used in historical buildings. Techniques have been developed in which lasers are utilized to relay details not only on the chemical composition of a historical building (which can help to deduce the materials used), but they can also identify micro-structure, morphological features, condition, and environmental impact on historical buildings, making it an invaluable technique for studying historical buildings.
Restoration and Conservation Relies on Material Identification
Historical architecture is fundamental to understanding the journey of civilization. It is of key anthropological interest, making the conservation and analysis of historical buildings invaluable. With the development of laser techniques, scientists have been able to devise reliable ways to assess building materials which leads to our understanding of previous building techniques and civilizations, as well as allowing us to preserve them effectively.
Laser Scanning in Building Analysis
Lasers emit and receive electromagnetic radiation that they produce themselves in order to gain insight on the nature of the structure the radiation is focused on. There are a variety of laser scanning techniques that have already been established, however they generally work through collected data, known as a ‘point cloud’, by assessing a number of points within a given range. This data is converted into a Cartesian coordinate system, providing a detailed view of surfaces that are the subject of examination. For this reason, laser surveys have been used for many years in the analysis of historical buildings.
This kind of technique has proven efficient in revealing humidity, cracks that aren’t visible to the naked eye, and even substrate changes in walls. Further to this, laser scanning has been used to uncover changes in material type through higher resolution mapping techniques. However, the most fruitful method of laser scanning for material identification has been shown to be laser-induced breakdown spectroscopy (LIBS).
Identifying Materials with Laser-Induced Breakdown Spectroscopy (LIBS)
Laser-induced breakdown spectroscopy (LIBS) has been shown through numerous research projects to be effective at classifying unknown materials used in historical buildings.
LIBS works through emitting high energy laser pulses onto the material to be examined. The pulse of energy excites the surface of the material, resulting in a tiny portion of smaller than can be recognized by the human eye being ablated, followed by the generation microseconds later of the luminous laser-induced plasma (LIP). The laser-induced breakdown is then detected through the identification of ionic and atomic emission lines in the elemental spectra. As a result, trace elements are able to be determined, aiding the process of material classification.
The success of this method has been confirmed repeatedly over the past couple of decades through experimental scenarios. LIBS has been shown to be reliable at identifying architectural heritage materials at a range of sites, studied by a variety of researchers. The material composition of building components such as stones, bricks, roof sheets, and even mural paintings have been successfully identified through using LIBS.
Researchers are using this technique not only for its reliability, but also for the benefits it has over alternatives. The method is essentially non-destructive, meaning that no sample needs to be removed from the site, which is of key importance when wanting to maintain a site of historical significance. In addition, the process is rapid, producing results in just a few seconds for single spot analysis. Further to this, the method can recognize a broad spectrum of elements, including lighter elements such as magnesium, sodium, nitrogen, carbon, and oxygen.
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