Wide-Angle Broadband Antireflection Coatings Prepared by Atomic Layer Deposition

Abstract

A novel broadband antireflective coating with ultra-low residual reflectance for light incidence angles from 0° up to 60° is presented. The system consists of an interference multilayer coating made by atomic layer deposition (ALD) combined with a low- n nanoporous SiO₂ top-layer obtained by wet-chemical etching of an atomically mixed SiO₂/Al₂O₃ ALD composite. The average residual reflectance measured at normal incidence for double-sided coated B270 glass substrates is only 0.5% in a broad spectral range from 400 to 1100 nm. The average reflectance of the substrate considering both front and rear sides decreased in the visible spectral range of 420-680 nm from 9.9 and 15.8 to 0.4 and 1.8% at an oblique angle of incidence (AOI) of 45° and 60°, respectively, by applying the hybrid ALD antireflection coatings. The measured average transmittance reaches 99.5% at AOI 6° in the 400-950 nm spectral range. Measurements three weeks after preparation show only a small reduction of the average transmittance to 99.3% in this spectral range spanning 550 nm. Ten months later, the average transmittance is still 99.0%, whereby the sample handling might have also affected the performance. The hybrid ALD system shows excellent conformal AR performance on a strongly curved B270 aspheric lens with a diameter of 50 mm and a height of 25 mm. The presented process is a promising route toward omnidirectional AR coatings on complex 3D optics, which are increasingly important for consumer and high-performance optical systems.