Finite-element-method study of tilt mirrors without PZTs using different clamping methods under laser irradiation

Abstract

Tilt mirrors play a fundamental role in correcting aberrations in adaptive optics systems. To analyze the influence of clamping methods and materials on temperature rising, deformations and high-order aberrations of tilt mirrors without PZTs during the evaluation of laser irradiation of multilayer coatings, a finite-element model of tilt mirror with a diameter of 100 mm and thicknesses of 12.5 mm was constructed. The deformation and high-order aberrations were simulated after applying a laser to the mirrors. The appearance of peak-to-valley and high-order aberrations became more significant as the tilt mirror was supported on the edge at 3 points 120° apart. Using 3 points at the back and 3 points on the side 120° apart with polytetrafluoroethylene (PTFE) protection clamping lessened the effect, and the PV was only 0.0828 µm. The corresponding 65th-order Zernike coefficients were lower, so the clamping approach is ideal for fixing the tilt mirror for evaluating the multilayer coatings. Also, the temperature rising and thermal deformation of tilt mirrors made from various materials under laser irradiation were calculated. The results show that the tilt mirror made of ultra-low expansion microcrystalline glass had the highest temperature rising and the lowest thermal deformation. The temperature rising and PV was 10.56 ℃ and 0.004 µm, respectively. Beryllium and silicon carbide materials are suitable for increasing the resonance frequency and reducing the weight of tilt mirrors. These results are also useful for designing the clamping methods of large size folding mirror, telescope fast steering mirror and small scanner mirror, etc.