Broadband Antireflection Coatings for Spaceflight Optics

C Cole

PhD Thesis - The University of Reading, Department of Cybernetics (1995)

Abstract

This thesis is a description of the research work carried out on the materials and design methods for spaceflight broadband anti-reflection coatings. These coatings are necessary to suppress image ghosting and reflection losses from the refractive optical components of planetary orbiting radiometers and solar system probes.

Broadband anti-reflection coatings are complex structures to design. Their wide spectral range of operation leads to the presence of many possible coating designs with the same approximate performance. Contemporary design methods are examined for the suitability in designing broadband, practical coatings. The need for a new synthesis method is identified, and its implementation is described in this thesis.

Coating materials must be highly transparent across the required spectral region and also mechanically robust enough to withstand the rigours of outer space. Coating materials for visible and infrared spaceflight coatings are described along with the experiments used to verify their space suitability.

A new synthesis method is described for the design of broadband anti-reflection coatings that aids the designer by indicating which transparent materials are available and what performance can be expected for the required spectral region, It is an evolutionary method that uses a complete layer thickness search routine and good starting designs in order to obtain the optimal design for the given design parameters. Examples are given of broadband anti-reflection coatings derived in this manner, such as the coatings for the HIRDLS atmosphere-monitoring instrument on the NASA EOS-Chem satellite and the CIRS instrument onboard the Cassini-Huygens probe to Saturn.

The effect of manufacturing errors on broadband anti-reflection coatings is also described. Both random and systematic errors are considered. The most error-sensitive layers are identified and the general tolerance of broadband anti-reflection coatings to errors is quantified in given examples.

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