Mechanism And Experimental Study On Laser Cleaning Of Contaminants From Opitcal Elements

Laser cleaning is a technology that uses laser-matter interaction to remove the contaminants from the surface of the object through direct or indirect ways. Compared with traditional cleaning technology, it has many advantages: it can clean different pollutants by adjusting the laser parameters; it is widely used and has high cleaning efficiency, pollution-free, low cost; and it can be used to clean the micron and submicron particulate pollutants.In the large scale high-power solid-state laser device, the damage threshold of the optical components is reduced after polluted by particles and grease and the final output flux can be seriously affected. So it is necessary to clean their contaminated surfaces. But it is difficult to remove tiny particles by traditional cleaning technology. In this paper, we choose the K9 glass surface contaminants as the object to do theoretical analysis and experimental research. Using laser dry cleaning method, and laser plasma shock wave cleaning method, we cleaned the particle contaminants on K9 glass surfaces. As comparison, this paper also uses plasma cleaning method to remove the particles and grease pollutants on K9 glass surface. The optical microscopy, UV-VIS spectrophotometer, image analysis software, and particle analyzer are used to analyze the clean effect. The main contents and conclusions are as follows:(1) Using a wavelength of 355 nm pulse laser irradiate the dust particles and Al2O3 particles on K9 glass directly. We detect its cleaning effect and analyze the influence of spot size, laser power and laser frequency. At last, we find the best process parameters to clean the dust contamination: the spot size is 3.4 mm2, the laser energy density is 4.3 J/cm2 and the laser pulse width is 10 ns. By these parameters, the K9 glass substrate can be cleaned with good cleaning effect, and without damage to its body. it can be used to clean the micron and submicron particulate pollutants.(2) Using laser plasma shock wave, the dust contaminants are cleaned on K9 glass surface, the result shows that it can cleaning the dust with a high efficiency. And we get the relationship between efficiency, distance and shots. The cleaning area and efficiency decreases rapidly with increasing distance. When the distance from laser focal point to the surface of the substrate is 1.0 mm, and the laser shots are 10, the best cleaning efficiency is obtained.(3) Making use of the radio frequency plasma cleaning, the cleaning effect for the silica particles and oil contaminants on K9 glass is analyzed. Compared with laser cleaning, the former has better effect. But radio frequency plasma is good at cleaning oil contaminants so it can be a supplement to the laser cleaning method.