Five layer narrow band position variable filters for sharp colours and ultra low emittance
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A simplified approach to creating narrow visible and near IR transmission bands with thin films is outlined utilising just five layers on glass, three of which are thin silver. These films have very high reflection at most wavelengths except for a narrow anti-reflection band where reflectance can be very close to zero and transmittance is close to 70%. In addition these properties are combined with IR reflectance approaching 99% for a very small thermal signature. Spatial variation of narrow band colour is easily achieved and is demonstrated with production of a simple wedge filter covering the full visible spectrum. Measured CIE colour contours in transmittance and reflectance are presented and spectral data on experimental films is compared with ideal models. Potential sources of small departures from ideal models are examined to assess the scope for future improvements.
KeywordsDielectric Layer Metal Layer Silver Layer Double Cavity Sharp Colour
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