Patent ID: 8233219

Claim:
An optical multilayer thin-film filter (OMTFF), comprising: a substrate that is transparent to at least visible light; a multilayer film on a surface of the substrate, the multilayer film comprising a plurality of alternatingly laminated thin-film layers of a high-refractive-index material and thin-film layers of a low-refractive-index material; and an uppermost layer on the multilayer film, the uppermost layer comprising either MgF 2 or LiF; wherein the multilayer film and uppermost layer are collectively transmissive to visible light and collectively reflective to infrared light; the high refractive-index material and low-refractive-index material are each respective oxides; an uppermost-but-two (n−2) layer of the multilayer film comprises the high-refractive-index material; an uppermost-but-one (n−1) layer of the multilayer film comprises the low-refractive-index material; the uppermost layer is an (n) layer formed on the (n−1) layer; the successive layers of the high-refractive-index material and of the low-refractive-index material in the multilayer film were formed under vacuum; the (n) layer was formed under vacuum preceded by a momentary vent to atmosphere to introduce atmospheric water vapor to the multilayer film; the (n) layer includes at least one oxide of MgF 2 or LiF, respectively, resulting from a reaction of MgF 2 or LiF, respectively, in the (n) layer with oxygen from at least the (n−1) and (n−2) layers such that at least a portion of the n layer has a predetermined transparency and electrical conductivity; and the (n−2) layer comprises an amount of Mg or Li, respectively, from the (n) layer that is less than half the amount of Mg or Li, respectively, that otherwise would be present in the (n−2) layer if formation of the (n) layer were not preceded by the momentary vent to atmosphere.