Study On Laser Damage And High-temperature Performance Of Sol-gel Film

For optical films,the higher the laser-induced damage threshold?LIDT?means the more energy density laser is needed to destroy it.It also has better laser damage resistance and can promote the development of laser system to higher power and energy.The film prepared by the sol-gel method is better than the physical method for laser damage.The refractive index of the sol-gel film is low.So the density of the film should be increased by annealing to improve the refractive index.However,high temperature greatly reduces the LIDT of sol-gel film,and also limits the application of high-power laser system in extreme environment.In this paper,through comparative studied the effects of additives,film materials and organic content of sol-gel film to understand the influence factors of the laser-induced damage mechanism and high-temperature performance.The method of improving the LIDT and high-temperature performance of sol-gel film was sought.Firstly,TiO₂ films were prepared with different additives.The advantages and disadvantages of acetacetone?ACAC?and diethanolamine?DEA?were analyzed and discussed in detail.And the effects of the double additives on the properties and LIDT of the film were also investigated by adding polyethylene glycol 200?PEG 200?.Then the experimental results and the theoretical calculation based on the laser-induced damage model showed that the LIDT of the sol-gel film was determined by the structure of the film and the additive properties,especially thermal conductivity.Secondly,the TiO₂ films with DEA and PEG 200 were annealed at different temperatures.It was found that the LIDT decreases with the increase of annealing temperature.The LIDT of the films annealed at 523 K and 623 K decreased by 72% and 76% compared with 353 K,respectively.It can be seen that the three dimensional network structure was continuously damaged,and the defect and the surface roughness was increasing due to the increase of annealing temperature.According to the LIDT results and damage morphologies,a structure evolution model of the films at different temperatures was proposed.However,some organic also remained in the film even if the annealing temperature exceeded the boiling point of the organic.It provided a possible way and theoretical basis for the preparation of high temperature resistant sol-gel films.Finally,the influencing factors of high-temperature performance of sol-gel films were studied through changing the kinds of film materials,precursors,additives,and annealing temperature.It was found that the Zr O2 film is better than that TiO₂ film in high-temperature performance.And the content and kinds of organic compounds had important effects on the optical properties,phase structure,surface morphology and LIDT of the sol-gel films annealed at high temperature.In the paper,the Zr O2 films with Zr OCl2·8H2O and copolymer of silicone and polyaldoxyl ether had the best LIDT and high-temperature performance.The LIDT of the Zr O2 films was 33.06 J/cm2.Moreover,the LIDT decreased by 35.39% and still reached 21.36 J/cm2 after 623 K high temperature annealing.At the same time,the film LIDT was tested at in-situ high temperature to learn the change of the film LIDT under the high temperature environment.