Supermirrors are produced by depositing alternating layers of strongly contrasting substances, such as nickel and titanium, on a smooth substrate. A single layer of high refractive index material (e.g. nickel) exhibits total external reflection at small grazing angles up to a critical angle θ θ c . For nickel with natural isotopic abundances, θ θ c in degrees is approximately 0.1 ⋅ ⋅ λ λ where λ λ is the neutron wavelength in Angstrom units.