Laser Damage Of Optical Thin Films Induced By Organic Contamination And Defect Coupling

With the rapid development of space technology,laser applications in vacuum and space are becoming increasingly popular.From ranging,metrology,altimetry,communications to optical reconnaissance,various laser systems are becoming increasingly important in space exploration,and in recent years,the resistance of optical thin film components to laser damage has become a key factor in their service life,as well as hindering the development of high power and high energy laser systems.Studies have shown that the laser damage threshold of optical thin films decreases significantly in vacuum and space environments.In addition,some large terrestrial laser systems require their key devices to operate in a space environment in order to transmit high power lasers.Inevitably,the internal components of the laser system will release some molecular gases which,together with ultraviolet light,charged particles and atomic oxygen,will produce contamination deposits on the surface of the optical system film,causing serious degradation of its performance and leading to reduced performance and service life of the optical system,or even devastating damage.Therefore,it is urgent and important to study the mechanism of laser-induced damage of optical films induced by organic pollution under vacuum environment and to improve the resistance to laser damage of optical film components.In this paper,we investigate the optical field enhancement of optical thin films caused by the mutual coupling between organic contamination and defects using a time-domain finite-difference method.The results show that the mutual coupling between organic contamination droplets and defects leads to the local enhancement of the optical field,which is enhanced as the distance between organic contamination droplets and defects decreases and the diameter of organic contamination droplets increases.In addition,the coupling effect between the organic contamination layer and the defect depends not only on the thickness of the organic contamination layer,but also on its refractive index.In short,the peak light field decreases with increasing the thickness of the organic contamination layer,while the opposite trend occurs with increasing the refractive index of the organic contamination layer.In order to solve the problems of reduced resistance to laser damage,reduced laser damage threshold and shortened service life of optical films under vacuum conditions,this paper analyses the inhibitory effect of protective layers on the damage caused by organic contamination and defect coupling in optical films,and proves through theory and experiment that coating protective layers on optical films can effectively improve the damage threshold of films;ion beam sputtering is used to analyse the changes in surface properties,density of defects,concentration of organic contaminants adsorbed on the film surface and laser damage threshold after ion beam etching of The changes in surface properties,density of defects,concentration of organic contaminants adsorbed on the surface of the film and laser damage threshold after ion beam etching of the outer layer of optical films of different thicknesses were analysed by ion beam sputtering,demonstrating that ion beam sputtering technology etching the outer layer of a certain thickness not only improves the surface quality of the film but also enhances the laser damage threshold of the film.