There are four main types of laser cleaning methods:

①Laser dry cleaning
　　A) The light beam emitted by the laser is absorbed by the contamination layer on the surface to be treated.
　　B) Absorption of large energy forms a rapidly expanding plasma (a highly ionized unstable gas), which generates shock waves.
　　C) The shock wave turns pollutants into fragments and is removed

②Laser + liquid film method
First deposit a layer of liquid film on the surface of the substrate, and then use laser radiation to decontaminate;

③Laser + inert gas method
While the laser is irradiated, use an inert gas to blow on the surface of the substrate. When the dirt is peeled off the surface, it will be blown off the surface by the gas immediately to avoid re-contamination and oxidation of the surface;

④Laser + chemical method
After using laser irradiation to loosen the dirt, clean it with non-corrosive chemical methods.
Currently, the first three methods are commonly used. The fourth method is only seen in the cleaning of stone cultural relics.
Compared with traditional cleaning methods such as mechanical friction cleaning, chemical corrosion cleaning, liquid solid strong impact cleaning, and high-frequency ultrasonic cleaning, laser cleaning has obvious advantages.

1. Introduction to laser

The English name of the laser is LASER, which is an acronym for "light amplification by stimulated emission of radiation".

2. The principle of laser generation

When the electrons in the atom absorb energy and then transition from a low energy level to a high energy level, and then fall back from a high energy level to a low energy level, the released energy is released in the form of photons. The photon beam (laser) that is lured (excited) has a highly consistent photon optical characteristic. Therefore, the laser has better monochromaticity, directivity and higher brightness than ordinary light sources.

3. Advantages of laser

Good monochromaticity: The wavelength distribution range of the light emitted by the laser is narrow, so the color is extremely pure. The monochromaticity of laser is far stronger than other monochromatic light sources.

Good monochromaticity can facilitate filtering and improve the signal-to-noise ratio. In material processing, the absorption spectra of different materials are different, and the monochromaticity of the laser can well control the absorption depth and distribution, and the materials can be processed selectively and in a controlled manner. Monochromatic light is much more convenient in optical design, there is no difference in dispersion, and the better the monochromaticity, the more stable the corresponding wavelength or frequency.

Strong directivity: The beam emitted by the laser only emits in one direction. Ordinary light sources are mostly scattered in all directions. If you want to make the light source converge to one part, you need to install auxiliary devices. For example, the headlight of a car is equipped with a light-gathering reflector to make the light converge and emit in one direction.

The laser light emitted by the laser is only emitted in one direction, and the divergence of the beam is extremely small, almost parallel. The distance between the earth and the moon is about 380,000 kilometers. If a beam of light is emitted to the moon, but the laser spot on the moon's surface is less than two kilometers, the seemingly parallel searchlight beams shoot toward the moon, and the spot diameter will cover the entire moon.

Good coherence: Coherence indicates the degree to which light easily interferes with each other. If light is considered as a wave, the closer the band, the higher the coherence. For example, when different waves on the water collide with each other, they may strengthen or cancel each other. As with this phenomenon, the more random the waves, the weaker the interference.

The phase, wavelength, and direction of the laser are the same, which can maintain a strong wave, so as to achieve long-distance transmission. Highly coherent light has the characteristics of long-distance transmission without spreading. It has the advantage of being able to gather into a small spot through the lens, and the generated light can be transmitted to other places and used as high-density light.