Tunable Physicochemical Properties And Its Performance Of Chemical Films

Sol-gel chemical films are widely used in the optical systems of high-energy laser devices due to their low preparation cost,excellent optical performance,and high laser damage threshold.With the continuous increase of the output power of laser devices,the service life and load capacity of optical components in laser devices have gradually become the bottleneck restricting the development of inertial confinement fusion.At present,there are two ways to improve the load capacity and service life of optical elements:(1)To improve the manufacturing and processing technology of optical components to reduce surface defects caused by processing,and reduce defect-induced damage.(2)To improve the service life and load capacity by the sol-gel antireflection film coated on the surface of the optical element with high laser damage threshold.However,since the chemical film is prepared by the sol-gel method,the particle diameter is generally tens of nanometers,and the film layer is mainly composed of nanosilica particles randomly stacked on the surface of the substrate.The membrane structure is loose and porous and there is no stable connection between particles.The surface of silica particles contains a lot of silanol,which is very easy to adsorb moisture and pollutants in the environment and reduce the performance of the film.To resolve the existing problems of chemical films,the post-treatment methods of ammonia,plasma and hexamethyldisilazane(HMDS)surface modification were used to adjust the physicochemical properties of chemical films.Appropriate post-treatment can enhance the mechanical properties,optical properties and environmental stability of the chemical film without damage to the function of the chemical film so as to greatly improve the service life of the chemical film in the vacuum operation environment of high-power solid-state laser device,and finally reduce the operation and maintenance costs.The main work and experimental results of this thesis are as follows:Ammonia surface modification was used to adjust the physical and chemical properties of the sol-gel antireflection film.The influences of different ammonia amounts and posttreatment times on the composition,optical properties,surface morphology and antipollution performance of the film were studied.The experimental results show that the antireflective film can not be effectively strengthened in a short time or by small amount of ammonia.A moderate amount of ammonia treatment can cause a large number of free hydroxyl groups on the surface of the film to undergo dehydration and condensation reactions,promote film shrinkage,and connect adjacent silica particles through stable chemical bonds to improve the mechanical properties of the film.The results of vacuum pollution experiments showed that the ammonia water postprocessing could significantly improve the antifouling performance of the sol-gel antireflective coating.However,with the increase of ammonia amount or post-treatment time,the alkaline humid environment improves the hydrophilicity of the film.The adsorption of pollutants on the film gradually decreased and tended to be stable.Plasma and HMDS surface modifications were used to adjust and control the performance of the sol-gel antireflection coating.The effects of plasma treatment on the optical properties,surface morphology,hydrophilic and hydrophobic properties of antireflective coatings were studied.After that,the HMDS surface modification and plasma treatment were combined to study the changes in the composition,optical properties,surface morphology,hydrophobicity and anti-pollution properties of the solgel antireflection film after the two-step post-treatment.During the plasma treatment process,the free radicals and high-energy particles interact with the surface of the film.The thickness of the film and the content of free hydroxyl in the film decreases.The transmission spectrum shows that the transmission peak shifts to the short wavelength.With the decrease of films thickness,the pores in the films become more open,and the water affinity of the films increases.However,as the processing time increases,the plasma etching effect begins to destroy the film structure,reduce the optical properties of the film,and even remove the film.After HMDS surface modification combined with plasma treatment,the surface and pores of the film were filled with trimethylsilicon.Two-step treatment increases the refractive index of the film and significantly improves the hydrophobic performance.Finally,the vacuum pollution experiment shows that the plasma-HMDS two-step post-treatment greatly improves the anti-pollution performance of the AR coating.