Multi-layer interference coatings
First Claim
1. A multi layer interference device having a reflectance spectrum comprising at least one maximum comprising;
- at least one multilayer stack, a reflective layer having at least one surface for carrying said at least one multi layer stack, said at least one multi layer stack comprises a first layer of dielectric material, a layer of absorbing material and a second layer of dielectric material arranged in series with the layer of absorbing material situated between the first and second layers of dielectric material, wherein the second layer of dielectric material has substantially the same optical thickness as the first layer of dielectric material at a wavelength substantially corresponding to a maximum in the reflectance spectrum and wherein the layer of absorbing material has a refractive index n and an optical constant k, such that incident electromagnetic radiation, having a wavelength at which odd multiples of half wavelengths substantially correspond to the optical thickness of the at least one multi layer stack at said wavelength, is substantially absorbed within the device, wherein the layer of absorbing material is a conductive substoichiometric metal oxide and in that the device has a reflectance spectrum in the infrared wavelength region.
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Accused Products
Abstract
A multi layer interference coating comprising at least one multi layer stack deposited on a reflective layer (9), wherein each multi layer stack comprises a first dielectric layer (11), a layer of asbsorbing material (10) and a second layer of dielectric material (11) arranged in series and having a reflectance spectrum in the infrared region comprising at least one maximum. The dielectric layers are of equal optical thickness and typically are of the same material. The multi layer structure of the coating is such that incident electromagnetic radition, for which odd multiples of half wavelengths correspond to the optical thickness of the multi layer coating at the incident wavelength do not propagate within the coating and reflection at these wavelengths, is suppressed. Coatings may therefore be designed to have a near satured color in the visible wavelength spectrum. The reflective layer may be a metal or a conducting oxide, a conducting nitride, a conducting silicide or a conducting sulphide. The absorbing layers may be Cr, V, Pd, Ni, Pt, conducting oxides, or substoichiometric metal oxides, such as TiOx. In one form of the coating, where a non-metal absorber is used, the second dielectric layer may be removed in at least one of the multi layer stacks. The coating may be incorporated in a system for verifying the authenticity of an article.
103 Citations
44 Claims
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1. A multi layer interference device having a reflectance spectrum comprising at least one maximum comprising;
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at least one multilayer stack, a reflective layer having at least one surface for carrying said at least one multi layer stack, said at least one multi layer stack comprises a first layer of dielectric material, a layer of absorbing material and a second layer of dielectric material arranged in series with the layer of absorbing material situated between the first and second layers of dielectric material, wherein the second layer of dielectric material has substantially the same optical thickness as the first layer of dielectric material at a wavelength substantially corresponding to a maximum in the reflectance spectrum and wherein the layer of absorbing material has a refractive index n and an optical constant k, such that incident electromagnetic radiation, having a wavelength at which odd multiples of half wavelengths substantially correspond to the optical thickness of the at least one multi layer stack at said wavelength, is substantially absorbed within the device, wherein the layer of absorbing material is a conductive substoichiometric metal oxide and in that the device has a reflectance spectrum in the infrared wavelength region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
the device of claim 1 wherein the device is applied to the article to be authenticated, an illuminator for illuminating the device with incident radiation comprising one or more wavelengths wherein one or more of the wavelengths substantially correspond to a maximum or a minimum in the reflectance spectrum of the device and a detector for detecting radiation reflected from the device at one or more of the wavelengths, whereby the detection of the reflected radiation provides an indication of the authenticity of the article.
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21. The system of claim 20, whereby a comparison of the reflected radiation at two or more wavelengths provides an indication of the authenticity of the article.
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22. The system of claim 20 wherein the detector for detecting infrared radiation reflected from the device is a thermal imager.
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23. The system of claim 20 wherein the detector for detecting infrared radiation reflected from the device is a spectrophotometer.
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24. A multi layer interference device, having a reflectance spectrum in the infrared wavelength region comprising at least one maximum, comprising;
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at least one multilayer stack, a reflective layer having at least one surface for carrying said at least one multi layer stack, wherein said at least one multi layer stack comprises a first layer of dielectric material, a layer of absorbing material and a second layer of dielectric material arranged in series with the layer of absorbing material situated between the first and second layers of dielectric material, wherein the second layer of dielectric material has substantially the same optical thickness as the first layer of dielectric material at a wavelength substantially corresponding to a maximum in the reflectance spectrum and wherein the layer of absorbing material has a refractive index n and an optical constant k, such that incident electromagnetic radiation, having a wavelength at which odd multiples of half wavelengths substantially correspond to the optical thickness of said at least one multi layer stack at said wavelength, is substantially absorbed within the device and wherein the layer of absorbing material is any one of a conducting oxide, a conducting nitride, a conducting silicide or a conducting sulphide for which the n/k ratio is substantially equal to 1 in the infrared wavelength region. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33)
the device of claim 29, wherein the device is applied to the article to be authenticated;
a temperature control for varying the temperature of the device such that the reflectance of the device at one or more wavelengths may be varied as the temperature is varied;
an illuminator for illuminating the device with infrared radiation comprising one or more wavelengths substantially corresponding to one or more of the wavelengths at which the reflectance varies and a detector for detecting infrared radiation reflected from the device at one or more wavelengths at which the reflectance varies, whereby a comparison of the reflected radiation before and after the temperature of the device is varied provides an indication of the authenticity of the article.
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31. The system of claim 30 wherein the means for illuminating the device and the temperature control is a single laser.
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32. The device of claim 24 wherein the absorbing material is substoichiometric vanadium dioxide (VO2−
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33. The device of claim 24 wherein the absorbing material is doped vanadium dioxide and the reflectance spectrum of the device may be varied with temperature.
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34. A multi layer interference device, having a reflectance spectrum in the infrared wavelength region comprising at least one maximum, comprising:
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at least one multilayer stack, a reflective layer having at least one surface for carrying said at least one multi layer stack, said at least one multi layer stack comprises a layer of dielectric material and a layer of absorbing material, wherein the layer of absorbing material has a refractive index n and an optical constant k, such that incident electromagnetic radiation, having a wavelength at which odd multiples of quarter wavelengths substantially correspond to the optical thickness of said at least one multi layer stack at said wavelength, is substantially absorbed within the device, wherein the layer of absorbing material is a non-metal absorbing material. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41, 42, 43)
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44. A multi layer interference device, having a reflectance spectrum in the visible wavelength region comprising at least one maximum, comprising;
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at least one multilayer stack, a reflective layer having at least one surface for carrying said at least one multi layer stack, said at least one multi layer stack comprises a layer of dielectric material and a layer of absorbing material, such that incident electromagnetic radiation, having a wavelength at which odd multiples of quarter wavelengths substantially correspond to the optical thickness of said at least one multi layer stack at said wavelength, is substantially absorbed within the device, wherein the absorbing material is a conducting substoichiometric metal oxide.
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Specification