STP799

    Dimensional Stability of Zerodur and ULE Mirrors Undergoing Thermal Cycling

    Published: Jan 1983


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    Abstract

    Zerodur and ULE quartz have been shown to have exceptional dimensional stability over extended time periods and to be insensitive to small temperature variations when they are maintained near room temperature. However, it is not clear what their dimensional stability will be after cycling through a more extended range of temperatures such as might occur during bakeout and film deposition when applying dielectric multilayer high-reflectance coatings. Since mirrors are required to maintain tolerances as severe as λ/100 visible equivalent in some laser applications, the safe limits for temperature cycling are of considerable interest, and a preliminary experiment was performed to investigate this question. During the experiment, a convenient method for interferometrically verifying the thermal expansion coefficient of these low-expansion materials was developed and will be described. In one series of experiments, a 6-inch-diameter Zerodur optical flat of the highest quality having a better than λ/40 average peak-to-valley optical figure was oven heated to a peak temperature and then allowed to cool in air. No permanent change was observed up to a temperature of 200°C, but at 250°C the mirror took a permanent set. After the 300°C cycle, this set increased to λ/5. Under similar conditions, the ULE sample was unaffected; it was then water quenched after heating, a much more severe test. Even at oven temperatures of 350°C, the ULE sample developed no permanent set. These experiments suggest that caution should be employed when heating Zerodur mirrors above 150 to 200°C. There is no comparable restriction on ULE mirrors.

    Keywords:

    expansion coefficient, fused quartz, optical figure, thermal distortion, ULE quartz, Zerodur


    Author Information:

    Shaffer, JJ
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Bennett, JM
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Bennett, HE
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California


    Paper ID: STP37254S

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37254S


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