STP799

    Effects of Undercoats and Overcoats on Damage Thresholds of 248 nm Coatings

    Published: Jan 1983


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    Abstract

    Previous experiments have demonstrated that 1064 nm high reflectors benefit from the addition of halfwave silica overcoats, and that 1064 nm antireflection coatings can be improved by adding halfwave silica undercoats or barrier layers. In each case, a statistical improvement of about 50% has been observed. This paper reports similar results for coatings designed for 248 nm. The high reflectors were scandia/magnesium fluoride quarterwave stacks. Three design variations were tested: with no overcoat, with a halfwave silica overcoat, and with a halfwave magnesium fluoride overcoat. The presence of the overcoat more than doubled the threshold of the reflectors. The highest threshold, 8.5 joules/sq.cm, was measured on a reflector with a magnesium fluoride overcoat. Two material combinations were used for the four-layer antireflection coatings: scandia/silica and scandia/magnesium fluoride. Each of these combinations was coated without a barrier layer, with a silica barrier layer, and with a magnesium fluoride barrier layer. The barrier layer was an undercoat with a halfwave optical thickness. Varying degrees of improvement in thresholds, ranging up to 50%, were found in all cases with barrier layers. The highest thresholds exceeded 6 joules/sq.cm for scandia/silica coatings with silica barrier layers.

    Keywords:

    antireflection coating, electric field, laser damage, laser reflector, optical coating, overcoat, undercoat


    Author Information:

    Tuttle Hart, T
    Optical Coating Laboratory, Inc., Santa Rosa, California

    Lichtenstein, TL
    Optical Coating Laboratory, Inc., Santa Rosa, California

    Carniglia, CK
    Optical Coating Laboratory, Inc., Santa Rosa, California

    Rainer, F
    Optical Coating Laboratory, Inc., Santa Rosa, California


    Paper ID: STP37258S

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37258S


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