Predicting achievable design performance of broadband antireflection coatings

An empirically derived formula, which can be used to predict the average residual reflection that can be expected from an antireflection (AR) coating design as a function of bandwidth, overall thickness, available indices of the coating materials, number of layers, etc., is presented. This formula can be a useful tool not only for the thin-film designer but also for the nondesigner or system engineer to estimate the performance limits of an AR coating for a given application before the design is accomplished. The general predictions are also found to be consistent with the results of two recent AR design competitions involving many independent investigators. Some insight with respect to the basic underlying principles of AR coatings can also be gleaned from the results and the process by which they are found.