Optical EngineeringComposite mirror surface deformation due to lay-up sequences within quasi-isotropic laminates
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We address surface accuracy issues associated with the thermal stability of continuous-fiber-reinforced quasi-isotropic composite mirrors. Thermally induced surface deformations in /n quasi-isotropic laminates, where n=3, 4, and 6, are numerically and experimentally investigated for the effects of stacking sequence and surface resin layers. Symmetric laminates and asymmetric laminates caused by the presence of surface resin layers for fiber print-through (FPT) mitigation are considered in numerical models to evaluate the surface characteristics due to thermal variance of T=16.6 °C (30 °F). Numerical results from finite element analyses reveal that the presence of an out-of-plane sinusoidal surface deformation pattern is inevitable in quasi-isotropic laminates, and the surface patterns are associated with stacking sequences within the laminates. Analyses assuming the thermal variance reveal that none of the /n laminates meet the diffraction-limited surface deformation requirement (20) for precision composite optics, with the mean average magnitude of surface deformation in /n symmetric laminates due to the thermal variance being 250 nm. Projections of this data further reveal that temperature variations must be maintained within ±2 °C to expect diffraction-limited performance. Similarly, tight control over moisture content will be required. Adding surface resin layers in quasi-isotropic laminates for FPT alleviation produces larger out-of-plane deformations than high-frequency surface variations due to FPT.