One compound that is commonly used for single layer antireflective
coatings for visible spectrum elements is magnesium
fluoride (MgF2). It has an index of refraction that is close to
optimal (~1.38 at 500 nm) and is easily deposited onto glass.
With carefully controlled process and substrate temperatures of
200° C to 250° C, a very robust coating can be applied, but
otherwise care must be taken while cleaning magnesium
fluoride-coated surfaces, as the coating can be rubbed off with
vigorous cleaning. A theoretical reflectance curve for a single
layer of MgF2 is shown in figure 2. The reflection gains at offnormal
angles of incidence are relatively small for single-layer
coatings, as shown in figure 3.