Support systems for testing thin meniscus optical mirrors
- Iranijad, B.; Parks, R. E.; Lam, P.
The principles of elastic structural behavior and superposition were used in conjunction with finite element analysis to find a suitable test support system for thin meniscus mirrors. The finite element method was used to calculate the deflections of a thi.n meniscus mirror supported by various mechanisms. The support systems were explicitly represented in the finite element model by including the forces and moments that are induced by the support system.
To minimize the number of finite element runs, the basic loading cases were analyzed one at a time, and the deflections in each case were fit to Zernike polynomials. To represent the effect of each support system on the optical surface, the basic loading cases were combined by using the appropriate proportions of the Zernike polynomial coefficients. The analytical results favored airbag support over other possible support systems. If the pressure in the airbag is varied in a controlled manner, optical errors maybe separated out from the mechanical errors caused by an imperfect support system even for optical elements of a very high diameter-to-thickness ratio or asymmetric shapes. Using holographic techniques, several sets of experimental results were obtained that strongly confirmed the analytical findings.
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