23 July 2008 Picometer resolution interferometric characterization of the dimensional stability of zero CTE CFRP
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Abstract
Highly stable but lightweight structural materials are essential for the realization of spaceborne optical instruments, for example telescopes. In terms of optical performance, usually tight tolerances on the absolute spacing between telescope mirrors have to be maintained from integration on ground to operation in final orbit. Furthermore, a certain stability of the telescope structure must typically be ensured in the measurement band. Particular challenging requirements have to be met for the LISA Mission (Laser Interferometer Space Antenna), where the spacing between primary and secondary mirror must be stable to a few picometers. Only few materials offer sufficient thermal stability to provide such performance. Candidates are for example Zerodur and Carbon-Fiber Reinforced Plastic (CFRP), where the latter is preferred in terms of mechanical stiffness and robustness. We are currently investigating the suitability of CFRP with respect to the LISA requirements by characterization of its dimensional stability with heterodyne laser interferometry. The special, highly symmetric interferometer setup offers a noise level of 2 pm/√Hz at 0.1Hz and above, and therefore represents a unique tool for this purpose. Various procedures for the determination of the coefficient of thermal expansion (CTE) have been investigated, both on a test sample with negative CTE, as well as on a CFRP tube specifically tuned to provide a theoretical zero expansion in the axial dimension.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jorge Cordero Machado, Jorge Cordero Machado, Thomas Heinrich, Thomas Heinrich, Thilo Schuldt, Thilo Schuldt, Martin Gohlke, Martin Gohlke, Stefano Lucarelli, Stefano Lucarelli, Dennis Weise, Dennis Weise, Ulrich Johann, Ulrich Johann, Achim Peters, Achim Peters, Claus Braxmaier, Claus Braxmaier, } "Picometer resolution interferometric characterization of the dimensional stability of zero CTE CFRP", Proc. SPIE 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 70183D (23 July 2008); doi: 10.1117/12.789495; https://doi.org/10.1117/12.789495
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