Browse Prior Art Database

Process to Provide Unit-Index Films in Multilayer Interference Coatings

IP.com Disclosure Number: IPCOM000037240D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 91K

Publishing Venue

IBM

Related People

Rosenbluth, AE: AUTHOR

Abstract

Disclosed is a process for incorporating unit-indexing air spaces into interference coatings as single layers within a stack. Such coatings can function over a very large spectral of angular range, and show extremely low residual absorption and scattering. (Image Omitted)

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Process to Provide Unit-Index Films in Multilayer Interference Coatings

Disclosed is a process for incorporating unit-indexing air spaces into interference coatings as single layers within a stack. Such coatings can function over a very large spectral of angular range, and show extremely low residual absorption and scattering.

(Image Omitted)

The refractive index of an air or vacuum space is unity; this is considerably lower than that of any solid film. An air film therefore provides a very large refractive index contrast within a multilayer stack. Large index contrast allows a specified performance to be obtained with fewer layers; reduced layer count, in turn, allows variation. The air film is free of absorption, scattering, and dispersion also, by permitting a reduced layer count, the air film indirectly lowers the total absorption, dispersion, and scattering of the remainder of the stack.

It has long been known that an air gap exhibits interesting interference properties in the regime of frustrated total reflection, where light can "tunnel" between two closely spaced prisms [1]. Multilayer interference coatings that exploit these phenomenon can be constructed using the process illustrated in Fig. 1, which is based on a conventional lift-off step. Here a reverse-pattern is exposed in a photoresist layer, a support film is deposited, and a support structure (such as a bordering wall) is left after resist removal. Alternatively, the central area of the support film can be e...