Anti-reflective coating for a transparent substrate

Claim 1

An antireflective coating for the transparent substrate of an optical component, in which said coating comprises at least two layers, one of which has a thickness of approximately λ/4 and the other a thickness of approximately λ/2, and in which said λ/2 layer is a composite layer comprising a basic layer and at least one inhomogeneity adjusting layer, wherein λ is the wavelength lying within the band of wavelengths in which reflectances are to be reduced; characterized in that (1) said basic layer has a thickness greater than said inhomogeneity adjusting layer, (2) said composite layer has a reflectance of R'min, wherein R'min is the minimum reflectance which is caused at approximately λ/2 thickness of the layer measured when only said composite layer is formed on a substrate having a lower refractive index than said composite layer, and (3) said composite layer has an equivalent inhomogeneity φ' having a value defined by the relationship φ<φ'<1.2 wherein: φ is the inhomogeneity of said substrate and said basic layer having a thickness of λ/2 and is defined by the equation ##EQU4## φ' is defined by the equation: ##EQU5## wherein: R min is the minimum reflectance of the optical component at thickness of λ/2, N s is the refractive index of said substrate; and said basic layer is composed of zirconium oxide.