Formation And Optical Properties Characterization Of Sol-gel Deposited TiO₂and Ta₂O₅Laser Thin Films

In this paper, systematic studys of the process to prepare TiO2and Ta2O5film by sol-gelmethod, the effects of different additives on the TiO2films, the effects of differentcomponents, preparation environment, film thickness and the heat treatment on Ta2O5filmwere made. In this method, tantalum source was relatively inexpensive TaCl5, whicheffectively reduced the cost of Ta2O5optical films, at the same time, the laser induceddamage threshold (LIDT) was high and this provides a new process for the preparation ofhigh power laser films.First, different additives were used to prepare uniform and stable TiO2sols; TiO2filmswere prepared by dip-coating method and were characterized systematically. The preparedTiO2films were uniform, smooth and had high transmittance. But the film TiO2-A hadhigher refractive index than film TiO2-D. For TiO2-A, the damage morphology is mainlymelting, and for TiO2-A, the damage morphology is mainly delamination.Then, we study the effect of different hydrolysis catalyst on Ta2O5sol and the effects ofratio of raw materials and environmental for films prepared on sol and films. As hydrolysiscatalyst, water, ammonia and hydrogen peroxide were added respectively to prepare Ta2O5sol, and the nature and film-forming properties of the sols were analyzed. After that, theeffects of acetylacetone (AcAc), nitric acid (HNO3), hydrogen peroxide (H2O2) on theperformance of the sol were studied, and also the effects of temperature and humidity onfilm properties were studied. The results showed that the films prepared with H2O2performance best. The molar ratio of each component should be controlled at n (TaCl5): n(CH3CH2OH): n (AcAc): n (HNO3): n (H2O2)=1:111:0.88~1.58:0~2.45:2.10~3.60.At last, the influence of film thickness and heat treatment on the film quality andperformance were studied. Optimized ratio of raw materials was selected to prepare the sol,the evolution of the sol were studied firstly, and the different films were characterized byUV-visible spectroscopy, atomic force microscopy, weak absorption and laser induceddamage threshold to study the change of film properties. With film thickness increase from73.1nm to345.8nm，Rq increase from0.77nm to2.21nm，weak absorption increasefrom15.1ppm to21.8ppm and induced damage threshold decrease from24.1J/cm2to19.6J/cm2. With the rising of heat treatment temperature, the transmittance gradually decreased,the refractive index increased, the roughness Rq is gradually increased while the LIDTdecreased.