CO2 laser additive manufacturing of multi-layer heterogeneous transparent films using TiO2 and SiO2 nanoparticles

CO2 laser additive manufacturing of multi-layer heterogeneous transparent films using anatase-TiO2 and SiO2 nanoparticles (NPs) is reported. The preparation of these films was carried out in two steps; corresponding to (i) evaporation of liquid, and (ii) sintering NPs to form transparent thin films on the quartz substrate. A heat transfer theoretical model was developed to select the proper laser processing parameters. Based on the anti-reflection coating (ARC) model, a 55 nm thickness of each layer; i.e., TiO2 and SiO2, was chosen to minimize the reflectance. The microstructural properties were determined using SEM and XRD analysis. UV/Vis/NIR spectrophotometry measurements show that the sintered films are highly transparent, with an average transmittance above 85% in some wavelength ranges. The effects of the sequence of the TiO2 and SiO2 layer deposition on the optical properties of films were investigated. The porosity, transmittance, and reflectance data were utilized to determine the optical constants, refraction index, and absorption index of the TiO2/SiO2 coatings. Our results provide a comprehensive understanding of the ARC properties of the TiO2/SiO2 coatings.