Abstract
Antireflection (AR) coatings are indispensable in numerous optical applications and are increasingly demanded on highly curved optical components. In this work, optical thin films of SiO2, Al2O3, TiO2 and Ta2O5 were prepared by atomic layer deposition (ALD), which is based on self-limiting surface reactions leading to a uniform film thickness on arbitrarily shaped surfaces. Al2O3/TiO2/SiO2 and Al2O3/Ta2O5/SiO2 AR coatings were successfully applied in the 400–750 nm and 400–700 nm spectral range, respectively. Less than 0.6% reflectance with an average of 0.3% has been measured on a fused silica hemispherical (half-ball) lens with 4 mm diameter along the entire lens surface at 0° angle of incidence. The reflectance on a large B270 aspherical lens with height of 25 mm and diameter of 50 mm decreased to less than 1% with an average reflectance < 0.3%. The results demonstrate that ALD is a promising technology for deposition of uniform optical layers on strongly curved lenses without complex in situ thickness monitoring.
Highlights
Most optical systems contain a large number of lenses or other optical elements
Thin films applied in precision optics are produced by physical vapor deposition (PVD) [5,6]
atomic layer deposition (ALD) processes for dielectric thin films have frequently been reported, whereas Al2 O3 is the most investigated ALD material [26,27]
Summary
Most optical systems contain a large number of lenses or other optical elements. Reflections at each interface reduce the intensity of the transmitted light and the overall efficiency of the systems. To achieve a better uniformity on curved substrates, complex technical modifications are necessary when using PVD methods, that includes f.e. the constant rotating and tilting of the lens during the deposition, with or without the usage of complicated shadowing masks [7,8,9,10] Antireflection nanostructures are another approach to reduce reflection losses at curved surfaces [11,12,13]. Atomic layer deposition (ALD) is an alternative and promising technology for uniform multilayer optical coatings [14,15,16,17,18]. A typical ALD cycle for the deposition of metal oxides oxides contains four steps: precursor pulse, inert gas purge, oxidizing pulse and inert gas purge.
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