Studied On Sol-gel Derived Silica Antireflective Coatings Modified By Polyether

Antireflective(AR) coatings, as one kind of optical thin films, are widely used on various optical components, such as solar cell and high-power laser system. In the practical application, it is expected that high transmittance of the films must not change with time and the films should have higher laser induced damage threshold, so that these optical film can be used in high power optical area.In this work, sol-gel technology was used to prepare antireflective optical film. Sol were first prepared by sol-gel method with tetraethyl silicate (TEOS) as precursor, ammonia(NH4OH) as catalyst and ethanol as solvent. Silica antireflective coatings were prepared by dip-coating process. The influences of reaction temperature, silica concentration and the dip-coated withdrawal rate on the performance of the films were studied. Then, modified silica films were prepared by silica sol doped with glycerol propoxylate. The hydrophobic property and laser induced damage resistance of the unmodified and modified silica films were compared.The results show the reaction temperature has an important impact on the optimum dip-coating time of sol, but the effect of the reaction temperature on the maximum transmittance of the films is not evident. Silica concentration has important influence on the antireflective wavelength scope of coatings. The films prepared by sol of 4.0% silica concentration give high transmittance at longer wavelength(1ω), the peak transmittance is beyond 99.5%. For a given wavelength, the transmittance of the coatings increases first, then decreases when increasing the withdrawal rate, maximum transmittance appears at around 100mm/min for the wavelength of 1053 nm. The surface roughness of the coatings is better at lower withdrawal rate.The modified silica films also have high transmittance at longer wavelength(1ω). The contact angle with water of the unmodified and modified silica films are 28.5o and 68.5o. Placed in the moist condition for 30 days, transmittance of the unmodified and modified silica films have a loss for 2.5% and 1.0% respectively. Namely, modified silica films excel unmodified films in the hydrophobic capability. All silica films modified with glycerol propoxylates of different molecular weight show higher laser induced damage threshold. The maximum percentage of improvement reaches approximately 40%.