Wide-Angle Broadband Antireflection Coatings Prepared by Atomic Layer Deposition

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Developing broadband antireflective (AR) coatings is crucial for enhancing optical system performance.
• Existing AR coatings often struggle with performance degradation at oblique angles of incidence and on complex geometries.
• Atomic Layer Deposition (ALD) offers precise control over thin-film fabrication, but achieving broadband, omnidirectional AR properties remains a challenge.

Purpose of the Study:

• To present a novel broadband antireflective coating with ultra-low residual reflectance.
• To evaluate the coating's performance across a wide range of light incidence angles (0° to 60°).
• To assess the durability and conformal applicability of the coating on complex 3D optical components.

Main Methods:

• Fabrication of a hybrid AR coating system combining multilayer interference coating via ALD with a nanoporous SiO2 top-layer.
• Creation of the nanoporous SiO2 layer through wet-chemical etching of an SiO2/Al2O3 ALD composite.
• Characterization of reflectance and transmittance across broad spectral ranges and various angles of incidence, including testing on aspheric lenses.

Main Results:

• Achieved average residual reflectance of only 0.5% at normal incidence for wavelengths from 400 to 1100 nm.
• Significantly reduced reflectance at oblique angles: from 9.9% and 15.8% down to 0.4% and 1.8% at 45° and 60° AOI, respectively.
• Measured average transmittance of 99.5% (AOI 6°, 400-950 nm) with excellent stability over 10 months (99.0% transmittance).
• Demonstrated excellent conformal AR performance on a 50 mm diameter, 25 mm height aspheric lens.

Conclusions:

• The hybrid ALD antireflective coating provides ultra-low reflectance over a broad spectral range and wide angles of incidence.
• The coating exhibits remarkable durability and conformal applicability on complex 3D optics.
• This technology presents a promising pathway for developing advanced omnidirectional AR coatings for diverse optical applications.