Optical Model of Broadband Anti-Reflective Surfaces Based on Random Nanoisland Masked Etching Process

Antireflection properties of a surface can be achieved when surface relief features smaller than a wavelength of light behave as a gradient index from air into the material. Sub-wavelength structures operate over a much broader angular and wavelength range compared to traditional thin film coatings. In this work, we discuss a randomized surface relief structure made using a mask of gold nanoislands with feature sizes that can be tuned to suit the wavelength range of interest. The nanoisland mask is translated into a surface relief structure in fused silica using an ICP-RIE (Inductively Coupled Plasma Reactive Ion Etching) process. Using variations in process parameters, the depth, lateral spacing, and shape of the surface relief can be tuned to optimize performance. We will discuss two optical models – effective medium theory and rigorous coupled wave analysis – and apply these models to simulate transmittance of the surface relief structure. The models will be related to transmission measurements of various antireflective surfaces.