Application of Laser Cleaning in Cultural Heritage Preservation
Cultural relics are the remains and traces left by human beings in the course of historical development. The protection and research of cultural relics are of great significance for people to understand human history, reveal the objective laws of social development, and promote social progress. The cultural relics that have been preserved until now have been exposed to the air for a long time, so their surfaces have various degrees of contaminants such as mold, dust, and insect stains. For many years, domestic and foreign cultural relics protection workers have carried out extensive research on the cleaning of surface contaminants on cultural relics. 
Traditional cleaning methods include mechanical cleaning, chemical cleaning, and ultrasonic cleaning, although they are widely used in the cleaning industry, their application is greatly limited in environmental protection and high precision requirements. Mechanical methods cannot meet the high cleanliness cleaning requirements, while chemical cleaning methods are prone to environmental pollution and can only achieve limited cleanliness; especially when the contaminant composition is complex, multiple cleaning agents must be used repeatedly to meet the surface cleanliness requirements. Ultrasonic cleaning is powerless against sub-micron-sized contaminants, the size of the cleaning tank limits the range and complexity of the cleaned parts, and drying the parts after cleaning is a major challenge. Laser cleaning technology, a new cleaning technology that has rapidly developed in the past decade, is gradually replacing traditional cleaning processes in many fields and has great application prospects. It can adapt to the cleaning of various surface contaminants, has minimal impact on the environment, and can also be done without damaging the base material.
Laser cleaning utilizes the characteristics of laser beams, whereby a focusing system can concentrate the laser beam into different spot diameters, allowing for convenient control of the laser energy required for cleaning. Laser energy can be concentrated in both time and space. Laser cleaning takes advantage of these features to effectively remove contaminants. 
Compared with traditional cleaning methods, laser cleaning technology has some unique advantages:
1. Laser cleaning is a selective cleaning, which means that it has selectivity for the object to be cleaned. This technology can leave the base material intact. For different types of contaminants on different surfaces of the base material, the laser parameters (such as spot size, single pulse energy, pulse width, and repetition rate) can be set to selectively clean the contaminants without damaging the base material.
2. Environmental friendliness of laser cleaning. The waste generated by laser cleaning is basically solid powder, with a small volume and easy to store, which causes minimal environmental pollution and is a "green" cleaning process.
3. Non-contact nature of laser cleaning. Traditional methods often involve close-range operation, with mechanical forces acting on the cleaned surface, which can easily damage the surface of the cleaned object. On the other hand, laser cleaning is a non-contact processing method that can conveniently be operated at a distance. It can be transmitted through optical fibers and combined with robots or manipulators to clean parts that are difficult to reach with traditional methods.
4. Laser cleaning can remove various types of contaminants from the surface of different materials to achieve very high levels of cleanliness. Laser cleaning has successfully been used to clean a variety of materials, including marble, limestone, sandstone, pottery, travertine, plaster, aluminum, bone, parchment, and organic materials, of different types of contaminants, including dust, dirt, rust, paint, oil, and grease.
5. Precise positioning is possible. The laser beam can be precisely positioned on the surface of the material to be cleaned, with the spot size adjustable from a few millimeters to 1 cm, allowing for the cleaning of irregular or hidden material surfaces. It can also be controlled by a computer, making the positioning even more precise and automated.
6. It can effectively remove microscopic particles with a size of less than 1 micron. Some pollutants may have a scale of micrometers or even sub-micrometers, such as dust particles generated during etching and plating processes in electronic printed circuit boards. Traditional methods are difficult to remove such pollutants. Success has been achieved in using short pulse ultraviolet lasers to remove small particles with a size of about 0.1 microns from the surface of an object, and it has been applied in industrial production.
7. Laser cleaning equipment can be used for a long time in a stable manner, and usually only requires electricity and maintenance costs. The operating cost is low, and it can conveniently be automated.
The application of laser cleaning technology in cultural relics mainly includes the following aspects:
1. Removing dirt and deposits: Laser cleaning technology can effectively remove dust, dirt, grease, etc. from the surface of cultural relics, without causing damage to the relics themselves. For example, for cultural relics that have been buried underground for a long time and have a lot of deposits on their surface, traditional cleaning methods are difficult to remove and may cause damage. However, laser cleaning technology can easily solve this problem.
2. Removing coatings and repair marks: Laser cleaning technology can remove coatings and repair marks from cultural relics, restoring them to their original state. During cultural relic restoration, laser cleaning technology can be used in conjunction with other restoration methods to improve restoration efficiency and effectiveness. 
3. Reveal details and hidden information: Laser cleaning technology can reveal the details and hidden information on cultural relics surfaces, providing more clues for cultural relics research. For example, for cultural relics with rich surface details such as painted or carved surfaces, laser cleaning technology can remove surface dirt, making hidden information visible.
