Single-layer anti-reflective coatings are especially popular
when anti-reflection in the infrared is desired. Because many of
the substrates used in infrared have higher indices of refraction
(i.e., silicon, germanium, gallium arsenide, indium arsenide),
there are many more choices for an optimal anti-reflective coating compound than for glasses. For example, the abovementioned infrared substrates all have indices of refraction close to 4. A single layer of zinc sulfide can be used to antireflect all of these substrates quite effectively