Abstract
A novel boomerang-like alumina based antireflective coating with ultra-low reflectance has been produced for light incidence angles form 0 up to 45°. Boomerang-like alumina nanostructures have been fabricated on the BK7 glass substrates by dip-coating and surface modification via hot water treatment. To achieve the lowest residual reflectance, the effect of dip-coating rate and hot-water temperature in the treatment process has been investigated and optimized. To further investigate the boomerang-like alumina nanostructure and extract its graded refractive index profile by fitting the measured reflectance spectrum with the simulated one, a simulation based on the finite-difference time-domain (FDTD) method has been performed. The average reflectance measured at normal incidence for double-sided coated BK7 glass substrates is only 0.3% in the visible spectral region. Considering both sides, the average reflectance of the substrate decreased in the spectral range of 400–700 nm down to 0.4% at incidence angles of 45° by applying the boomerang-like alumina antireflection coatings. The optimized single layer boomerang-like alumina coating on the curved aspheric lens exhibited a low average reflectance of less than 0.14% and an average transmittance of above 99.3% at normal incidence. The presented process is a simple and cost-effective route towards broadband and omnidirectional antireflection coatings, which have promising potential to be applied on substrates having large scales with complex geometric shapes.
Highlights
A novel boomerang-like alumina based antireflective coating with ultra-low reflectance has been produced for light incidence angles form 0 up to 45°
The multifunctional broadband antireflective coatings are commonly prepared by physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques such as plasma-enhanced CVD, sputtering and e vaporation[4,5,6]
A low reflectance with an average reflectance of less than 0.3% was realized in the visible spectral region at normal incidence for the boomerang-like alumina nanostructures fabricated with a rate of 2 mm/s (~ 200 nm) and a hot water treatment temperature of 67 °C
Summary
A novel boomerang-like alumina based antireflective coating with ultra-low reflectance has been produced for light incidence angles form 0 up to 45°. Boomerang-like alumina nanostructures have been fabricated on the BK7 glass substrates by dip-coating and surface modification via hot water treatment. The average reflectance measured at normal incidence for double-sided coated BK7 glass substrates is only 0.3% in the visible spectral region Considering both sides, the average reflectance of the substrate decreased in the spectral range of 400–700 nm down to 0.4% at incidence angles of 45° by applying the boomerang-like alumina antireflection coatings. To achieve a broadband anti-reflective coating, the key issue is to avoid sharp changes in the effective refractive index between the air and the substrate. These methods capabilities are limited to constrained geometric shapes, such as cylinders or convex lenses
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