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    Effect of Anisotropic Stress on Thin Flim Damage Thresholds

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    Damage thresholds for silica/titania multilayer reflectors are measured using single, 30 ps, Nd:YAG laser pulses to study the effect of anisotropic stress on thin film performance. Damage testing sites near the edges of coatings were used to spatially correlate damage with reproducible anisotropic stress profiles taken parallel to the edge.

    Anisotropic stress in a coating is stress which has a directional dependence in the plane of the film. A microscope based modulated ellipsometer is used to measure anisotropic stress via induced birefringence. The damage testing system centers around a vertical illumination microscope. The damage pulse is directed by a 45° high reflector in the microscope tube section through a low power objective. The sample surface is viewed through the same objective used to focus the laser to 8 μm FWHM in the center of the viewing field. The goal is to spatially relate this data with microscopic stress measurements.

    In most cases, negative anisotropic stress areas are found to have lower damage thresholds while positive anisotropic stress correlates well with high damage threshold. Damage thresholds for uniform striplike areas of film are found to change dramatically compared to adjacent strips. In one case average damage threshold changed from 1.3 to 6.9 J/cm2 within 100 μm. The width of measured threshold bands in this work ranged from 0.5 to 2.5 J/cm2.


    Anisotropic Stress, Ellipsometry, Microscope-laser integration, Picosecond laser induced damage, Thin films

    Author Information:

    Heiney, AJ
    Allied Corporation, Mt. Bethel, NJ

    Eastman, J
    University of Rochester, Rochester, NY

    Gabel, CW
    University of Rochester, Rochester, NY

    Committee/Subcommittee: F01.19

    DOI: 10.1520/STP23132S