Optical Surface Laser Cleaning Technology Research

Laser cleaning technique is used to remove the pollutions from the surface of contaminated objects by the laser pulse irradiation. Laser cleaning can remove different contaminations on the different substrate surfaces by adjusting laser wavelength, pulse width, irradiation time and interaction mode, so it is a versatile technology and can solve the pollution troubles which can not be solved by the conventional cleaning methods. Compared with the conventional cleaning methods, laser cleaning has some advantages, e.g., without extra pollution, high efficiency and low cost. Therefore, it is widely investigated and applied.Because the conventional cleaning methods can not clean the gratings and on-line optics, the thesis mainly focuses on laser cleaning and laser induced plasma shockwave cleaning of optics by the theoretical and experimental investigations. It provides a new approach for the cleaning of gratings in chirped pulsed amplification (CPA) laser facilities and on-line cleaning of optics in high power solid-state laser facilities. The main contents of the thesis can be summarized as follows:(1) The laser dry cleaning model of particle contaminations has been constructed. The excimer laser (248 nm) cleaning process of Al2O3 particles on the Si substrate has been simulated. The relationships between time and substrate surface position, velocity and acceleration have been calculated. The laser cleaning thresholds of particles with different diameters and the laser induced damage thresholds induced by particle contaminations of the substrate have been calculated at the different laser pulse widths.(2) The laser induced plasma shockwave cleaning model of particle contaminations has been constructed. The plasma shockwave cleaning processes of SiO2 particles on the K9 glass and gold-coated K9 glass have been simulated, respectively. The relationships between cleaning efficiency and parameters (e.g., laser parameters, particle position) have been obtained.(3) The laser cleaning model of grease contaminations has been constructed. The CO2 laser cleaning process of the dimethylsilicone contamination on the gold-coated K9 glass surface has been simulated. The relationships between temperature and laser power, irradiation time have been calculated.(4) The laser induced plasma shockwave cleaning of SiO2 particles on the K9 glass and gold-coated K9 glass surface have experimentally been investigated, respectively. The curves of removal ratio versus particle position, laser gap distance and laser energy have been obtained. The removal ratio on the K9 glass surface can reach above 90% and the removal ratio on the gold-coated K9 glass surface can reach above 95%. The results show that the method can effectively remove the SiO2 particles and the experimental results are consistent with the simulated ones.(5) The CO2 laser cleaning of the dimethylsilicone contamination on the gold-coated K9 glass surface has experimentally been investigated. The curves of cleaning efficiency versus laser power, irradiation time have been obtained. The results show that the cleaning area increases with the increase of radiation time and laser power on condition that the gold-coated K9 glasses are not damaged. The cleaning area doesn't change much with the variation of laser frequency. The experimental results are consistent with the simulated ones.The theoritical and experimental results show that laser cleaning is an effective cleaning method to remove particles and grease contaminations on the optics surface. It can also be used for grating cleaning and on-line cleaning of optics. In addition, the technique has wide applications in other fields.