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Surface figure changes due to thermal cycling hysteresis
Applied Optics
|June 5, 2010
Summary
Thermal cycling hysteresis can distort mirror surfaces, especially with nonuniform heating. Standard Zerodur showed distortions, but a new experimental Zerodur and other materials like ULE and Cer-Vit did not exhibit this hysteresis effect.
Area of Science:
- Materials Science
- Optical Engineering
- Thermal Analysis
Background:
- Low expansivity mirror substrates are critical for high-precision optics.
- Thermal cycling can induce stresses and affect the surface figure of optical components.
- Understanding material behavior under thermal stress is essential for mirror substrate selection.
Purpose of the Study:
- To investigate the impact of thermal cycling hysteresis on the surface figure of low expansivity mirror substrates.
- To identify which materials exhibit hysteresis and under what heating conditions.
- To evaluate potential solutions for mitigating hysteresis-induced distortions.
Main Methods:
- Thermally cycled 20.3-cm (8-in.) diameter mirrors and dilatometer samples made of Zerodur, ULE, and Cer-Vit.
- Applied thermal cycling rates of 6 K/h and 60 K/h.
- Utilized both uniform and nonuniform heating methods.
Main Results:
- Figure distortions up to lambda/10 were observed exclusively with nonuniform heating of standard Zerodur.
- Standard Zerodur was the only material exhibiting measurable thermal hysteresis.
- A new experimental formulation of Zerodur demonstrated no thermal hysteresis.
Conclusions:
- Nonuniform heating during thermal cycling is the primary cause of surface figure distortion in standard Zerodur substrates due to thermal hysteresis.
- ULE and Cer-Vit materials, along with the new experimental Zerodur, are more robust against thermal cycling hysteresis.
- Material selection and controlled heating are crucial for maintaining surface figure integrity in precision optics.
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