How does thermal cycling hysteresis affect surface figure in low expansivity mirror substrates? Zerodur, ULE, and Cer-Vit 20.3-cm (8-in.) diam mirrors and dilatometer samples were thermally cycled at 6 and 60 K/h with uniform and nonuniform heating. Figure distortions as large as lambda/10 were observed only with nonuniform heating of standard Zerodur, which was the only material exhibiting thermal hysteresis. A new experimental Zerodur appears to be free of this problem.
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Jacobs et al. (1987) studied this question.
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