Page "Anti-reflective coating" Paragraph 35

Further reduction is possible by using multiple coating layers, designed such that reflections from the surfaces undergo maximum destructive interference.

One way to do this is to add a second quarter-wave thick higher-index layer between the low-index layer and the substrate.

The reflection from all three interfaces produces destructive interference and anti-reflection.

Other techniques use varying thicknesses of the coatings.

By using two or more layers, each of a material chosen to give the best possible match of the desired refractive index and dispersion, broadband anti-reflection coatings which cover the visible range ( 400 – 700 nm ) with maximum reflectivities of less than 0. 5 % are commonly achievable.