Infrared optical filters for the infrared atmospheric sounding interferometer meteorological space instrument.

Optical coatings are designed and produced for the Infrared Atmospheric Sounding Interferometer meteorological space instrument operating in the spectral range 3.5 15.5 m. First we discuss the choice of substrates and determine the complex refractive indices of thin-film materials. Then several theoretical solutions are studied for optimizing the efficiency of the instrument. To allow us to study the feasibility of the coatings, a specific mid-infrared optical monitoring system has been developed. This system is validated by the successful manufacture of two-cavity Fabry Perot filters.

Analytical achromatic design of metal-dielectric absorbers.

Metal-dielectric coatings can be used successfully to design broadband absorbers. However, the understanding of the designs is not easy. Here we present a new analytical method using achromatic three-layer stacks. Such metal-dielectric basic structures permit movement from a fixed admittance value to another one over a wide spectral range. Efficient designs are calculated and explained with this method.

Design and Manufacture of Low-Absorption ZnS-YF(3) Antireflection Coatings in the 3.5-16-num Spectral Range.

Broadband antireflection coatings on ZnSe substrates are designed and manufactured in the 3.5-16-mum IR range. The thin-film materials are YF(3) and ZnS produced by electron-beam deposition. To reach optimal performances to as great as 16 mum, we performed an accurate determination of complex indices, taking into account dispersion laws and absorption due to water within layers. With this knowledge, designs are optimized and absorption is reduced at 16 mum.

Optical coating without phase dispersion for a Fabry-Perot interferometer.

Phase dispersion induced by coatings can be a critical phenomenon in interferometry. We are interested in special mirrors intended for a Fabry-Perot interferometer with a high reflectance region and a low reflectance region in which phase dispersion on reflection must be avoided. We describe how a classical approach that uses the concepts of admittance and symmetrical multilayers allows the design of simple solutions.

Buffer layers for the design of broadband optical filters.

The use of buffer layers is a promising technique in the attempts developed for the design of optical multilayer coatings when two widely separated spectral regions are under consideration. Here we show that the buffer layer, associated with matching layers as in the application mentioned above, can also be exploited in a successive step process to broaden the spectral bandwidth of beam splitters or antireflection coatings.