Preparation of double-layer two wavelength infrared antireflective coating on CdSe substrate

Abstract Designing and fabrication of the infrared antireflection coatings are quite important for the application of infrared optical elements. Herein, double-layer two wavelength infrared antireflective (AR) coating was prepared on CdSe substrate by sol-gel method, in which the bottom layer is porous TiO2 film and the top layer is SiO2 nanoparticle film containing a small amount of TiO2 (molar ratio of Si/Ti is 7.7). The reflectivity of the coated sample is about 2.1% at 2000 nm and 2.8% at 2500 nm, respectively, and the average reflectivity of the whole wide band from 1800 nm to 2600 nm is about 2.6%, which is about 27% lower than that of uncoated CdSe substrate. By adding reasonable additives and designing the film structure, the problem that thick infrared film is not resistant to high temperature annealing was solved. Moreover, the AR coating shows a super hydrophilicity, which can avoid the influence of water mist condensation on the transmittance. Importantly, this AR coating exhibits a good thermal shock resistance, and the reflection spectrum of the film did not change after ten thermal shock cycles at 400 °C, which meaning this film can be expected to meet the requirements of high temperature irradiation environment. This work provides important guidance for the preparation of infrared AR film with high thermal stability.