Research On Laser And Multi-method Assisted Cleaning Technology For Coated Optical Elements

As a new cleaning technology,laser cleaning can effectively clean micro and sub-micron particles on the surface of the substrate without damage and can be used in the online cleaning of optical components.The coated optical components with sol-gel SiO₂ high transmittance flim are widely used in the high power laser systems.In high power laser systems,contaminant is easily absorbed on the film surface,which is mainly organic,mineral or metal particle.The contaminated particles not only reduces the optical performance of optical component,but also seriously affects the final output laser fluence.This thesis aims at the contaminated particles on the surface of the coated optical elements.The methods of single-shot dry laser cleaning and assisted laser cleaning are used to study online cleaning.The cleaning effects and critical process paremeters were discussed.In addition,the source of metal contamination on optical surfaces was studied based on laser cleaning method.The main research contents and conclusions are as follows:?1?The theoretical model of removing SiO₂ particle on optical surface by single-shot dry laser cleaning method was established.The numerical calculation and finite element analytical simulation were used to conduct a comparative study on the transient thermal expansion effect during the cleaning process.The relationship between the temperature distribution and thermal stress with time and laser flux were obtained,and the cleaning process intervals were predicted.?2?A Q switched pulsed laser with wavelength of 355nm and pulse width of 10ns was used to clean the mainly typical SiO₂ particles on coated Corning 7980 fused silica,large aperture vacuum isolation component and diffrent contamination on dielectric coated grating.Through the analysis of different laser parameters on the cleaning effect during single-shot dry laser cleaning,process parameters that can be used for online cleaning were obtained.The cleaning effect is wondeful without damaging the substrate.?3?The method of airflow displacement system assisted laser cleaning and backward incidence laser cleaning was used to remove the SiO₂ particles on the surface of coated Corning 7980 fused silica and large aperture vacuum isolation component.The results was compared to previous experiments.The study showed that the addition of multi-method assisted laser cleaning obviously increased the particle removal ratio and improved the quality of laser cleaning.?4?The surface of AA5083,AA6061 and AA7075 aluminum alloy irradiated with pulsed laser at low fluences were used to simulate the scattering laser in high power laser systems.The results showed that AA7075 aluminum alloy had the best laser resistance among the three samples.The laser pretreatment method further effectively reduced the metal particle generation.The metal contamination on the optical surface were controlled at source.