Wide band anti-reflection coating and article coated therewith

Claim 2

An article as in claim 1 wherein the anti-reflection coating has six layers comprising additional fifth and sixth layers formed respectively of low and high index materials, the thickness of the fifth and sixth layers being such that they yield a reflectance which is achieved by a single layer of equal optical thickness and having an index of refraction intermediate that of the low and high index materials utilized for the fifth and sixth layers.

Claim 3

In an optical element for use in an ambient medium in a waveband of approximately 380 to 660 millimicrons, a substrate having a normal light reflecting surface and an anti-reflection coating disposed on said surface and exposed to the medium, said anti-reflection coating comprising first, second, third, fourth, fifth and sixth layers counting in a direction from the medium and being formed of materials having high and low indices of refraction and being substantially absorption-free in the blue And ultra-violet region, said low index material being magnesium fluoride and said high index material being zirconium oxide, said first and second layers being formed respectively of low and high index materials and said third and fourth layers being formed respectively of low and high index materials, said fifth and sixth layers being formed respectively of low and high index materials, each of said second, third and fourth layers having an optical thickness which does not exceed one-quarter of the wave length of energy at a frequency within the waveband, said fifth and sixth layers having a combined optical thickness such that they yield a reflectance which is achieved by a single layer of equal optical thickness and having an index of refraction intermediate that of the low and high index materials utilized for the fifth and sixth layers, said layers formed of zirconium oxide each having a thickness which does not exceed approximately 500 Angstroms.