Nanoscale etching of microporous coatings for broadband antireflection coatings

Abstract

Broadband antireflection coatings are of great scientific and technological significance in optical areas because of their high transmission in broad wavelength bands. Here, we report an effective and simple approach to create broadband antireflection coatings based on nanoscale etching. To acquire broadband antireflection coatings, coatings with homogenously distributed pores were prepared by thermal treatment of polymer doped silica coatings and then were subjected to aqueous etching. The aqueous etching had selectivity along the thickness of the coatings, resulting in a graded porous morphology with more porosity on the top and less porosity at the bottom. The coatings with graded porosity exhibited excellent broadband antireflection likely due to the graded refractive index. The transmission of the coatings could be controlled by varying the amount of the polymer additives and the coating thickness. The optimized coating showed transmittance higher than 98% from 350 to 1100 nm, which is comparable to current state-of-the-art broadband antireflection coatings. The aqueous etching based approach enables easy access to broadband antireflection coatings on a wide range of optical substrates, and presents a promising alternative to existing technologies for fabrication of broadband antireflection coatings.