Importance

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Abstract

An interference filter, also referred to as a notch filter, of the type which reflects a certain wavelength range while letting pass over wavelengths bands of a range is disclosed. The filter is designed for operation in the visual and infra-red regions of the electromagnetic spectrum and in the disclosure the uniform layer pairs of material are such that the optical thickness of each layer of the or each layer pair deposited on a plane light-transmitting substrate is a non quarter-wave unequal thickness with respect to its complementary layer. Each layer pair has an overall optical thickness adding up to in total a half-wave thickness. The technique of degrading a standard quarter wavelength layer is also employed on a curved surface substrate with non-uniform layers, where one layer of a layer pair increases from the center to the periphery of the substrate and the other layer of the pair decreases from the center to the periphery of the substrate; a half-wave optical thickness being maintained throughout the layer pair.

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First Claim