STP954: Assessment of Optical Coatings Prepared by Molecular Beam Techniques

    Lewis, KL
    Royal Signals and Radar Establishment, Malvern, Worcestershire

    Savage, JA
    Royal Signals and Radar Establishment, Malvern, Worcestershire

    Cullis, AG
    Royal Signals and Radar Establishment, Malvern, Worcestershire

    Chew, NG
    Royal Signals and Radar Establishment, Malvern, Worcestershire

    Charlwood, L
    Royal Signals and Radar Establishment, Malvern, Worcestershire

    Craig, DW
    Royal Signals and Radar Establishment, Malvern, Worcestershire

    Pages: 9    Published: Jan 1986


    Abstract

    Thin films of ZnSe and other materials have been produced by molecular beam techniques in an ultra-high vacuum facility dedicated to the examination of fundamental aspects of thin film technology as applied to optical coatings. The ZnSe films have negligible values of absorptance at 10.6 μm and have laser damage thresholds in the range 35–38J/cm2, a significantly higher energy density than hitherto reported for ZnSe films. Examination of the films in cross section by high resolution transmission electron microscopy has revealed a polycrystalline columnar morphology, with the crystallite size dependent on deposition temperature. A complete absence of intergranular voids is noted which renders the film impervious to the ingress of water and other impurities when exposed to the atmosphere. This feature, together with the inherently high purity of the film is believed to be the factor responsible for the enhancement in laser damage threshold.

    The electron micrographs do however reveal sub-grain structure in the form of stacking faults and twin planes which are potential sinks for residual impurities in the material. Further improvements in damage threshold may be possible by elimination of this sub-grain structure.


    Paper ID: STP23118S

    Committee/Subcommittee: F01.19

    DOI: 10.1520/STP23118S


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