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    Recent Damage Results on High Reflector Coatings at 355 nm

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    Several studies of damage induced by 0.6 ns, 355 nm laser pulses have been carried out on thin-film reflectors. The reflectors consisted of dielectric materials vacuumdeposited onto BK7 substrate by evaporation. Each part was damage tested on several sites using one laser shot per site.

    Quarterwave stacks of various material combinations were used to make a series of reflectors. Four to six parts were tested for each of four materials combinations. The average damage thresholds obtained for these coatings were 3.5 J/sq. cm for scandia/magnesium fluoride, 3.0 J/sq. cm for zirconia/silica, 2.4 J/sq. cm for tantala/silica and 1 J/sq. cm for hafnia/silica. Interestingly, there was no improvement in those reflectors to which a halfwave silica overcoat was added. This is contrary to previous results at 1064 nm and 248 nm.

    A series of zirconia/silica reflectors was made using coating temperatures ranging from 150°C to 300°C. The thresholds were slightly improved by coating at higher temperatures.

    Coatings made of zirconia/silica with outer quarterwave layers of samarium fluoride and either silica or magnesium fluoride were also tested. Thresholds for these coatings ranged from 1.7 to 2.8 J/sq. cm and were slightly lower than the thresholds of the zirconia/silica stacks alone.

    Scandia/magnesium fluoride coatings with non-quarterwave designs have been shown to be effective in raising the damage threshold of high reflectors at 248 nm. Such designs reduce the electric field intensity in the outer scandia layers. The damage thresholds of several non-quarterwave designs were compared. The highest threshold, 5.1 J/sq. cm, was achieved by reducing the electric field in the two outer scandia layers.


    damage, electric field, high energy laser, laser damage, reflectors, thin film

    Author Information:

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

    Hart, TT
    Optical Coating Laboratory, Inc., Santa Rosa, CA

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

    Staggs, MC
    Optical Coating Laboratory, Inc., Santa Rosa, CA

    Committee/Subcommittee: F01.19

    DOI: 10.1520/STP28988S