Scalable, cost-effective, high-actuator-count deformable mirrors for astronomical adaptive optics

在过去的十年中，自适应光学（AO）已成为不可或缺的手段，以补偿大气湍流引入的大型地面望远镜的像差。由此产生的分辨率提高对大型望远镜尤为重要。 事实上，由于其更大的孔径，大型地面望远镜在狭窄的领域已经超过了轨道天文台可能的保真度，并导致了令人兴奋的最新进展，在观测系外行星，行星环和大气层的特性，以及银河系结构的研究。 允许这种波前补偿的通用光学部件是可变形反射镜（DM），其必须在1 kHz以上的频率下操作，并且其致动器计数与望远镜主反射镜的面积成比例。 事实上，计划中的超大望远镜（ELT）需要具有数万个致动器的DM-孔径大于20米的望远镜。 制造高致动器密度DM的技术具有高生产良率并因此具有低成本，目前还不存在。T博士计划的一个主要工作目标。波士顿大学的Bifano将使用微机电系统（MEMS）方法开发这种制造技术。 当前大尺寸DM的一个关键故障模式是数千条脆弱的电迹线，这些电迹线从位于模块外围附近的焊盘沿前表面沿着路由信号。 这个问题随着致动器数量的增加而迅速恶化，最后在为双子座行星成像仪（GPI）构建高计数DM的最新尝试中，产量不到1%。 Bifano博士的计划，以规避这一问题，涉及取代密集网络的表面走线与贯穿晶圆互连和键合到背面封装。 虽然这种基本技术在现代电子制造中并非前所未有，但技术挑战包括硅衬底必须承受非常大的电压（~ 250 V）以实现所需的~3.5微米的DM行程。 然而，回报是巨大的，因为可靠的高致动器数DM的可用性将催化有前途的成像技术，如多目标AO和极端AO的进步。拟议项目的成果将是具有2048个致动器的全功能MEMS DM原型，在领先的天文AO测试台上进行评估。 用于下一代AO的高致动器数DM的开发资金由NSF天文科学部通过其先进技术和仪器计划提供。

Over the past decade, adaptive optics (AO) has become indispensible as a means to compensate for aberrations introduced by atmospheric turbulence in large ground-based telescopes. The resulting gains in resolution are especially important for large telescopes. Indeed, because of their greater aperture, large ground-based telescopes have exceeded in narrow fields the fidelity possible with orbiting observatories and have led to exciting recent advances in the observation of exoplanets, characterization of planetary rings and atmospheres, and studies of galactic structure. The universal optical component that allows for this wavefront compensation is a deformable mirror (DM), which must operate at frequencies above 1 kHz and whose actuator count scales with the area of the telescope primary mirror. Indeed, DMs with tens of thousands of actuators are required for planned extremely large telescopes (ELTs) - those with apertures greater than ~20-m. The technology to make high-actuator density DMs with high production yield and therefore low cost does not exist today. A main objective of work planned by Dr. T. Bifano of Boston University is to develop such manufacturing technologies using a microelectromechanical systems (MEMS) approach. A critical failure mode of current large-format DMs has been the thousands of fragile electrical traces that route signals along the front surface from bonding pads located near the periphery of the module. This problem worsens rapidly as the actuator count increases, culminating in a yield of less than 1% for the latest attempts at constructing a high-count DM for the Gemini Planet Imager (GPI). Dr. Bifano's plans to circumvent this problem involve replacing the dense network of surface traces with through-wafer interconnects and bonding to a backside package. While this basic technique is not unprecedented in modern electronics manufacturing, technical challenges include the very large voltages (~250V) that must be endured by the silicon substrate to achieve the required DM stroke of ~3.5 microns. However, the payoff is large, since the availability of reliable high-actuator-count DMs would catalyze advances in promising imaging techniques such as Multi-Object AO and Extreme AO. An outcome of the proposed project will be fully functional MEMS DM prototypes with 2048 actuators, evaluated at a leading astronomical AO test bed. Funding for development high actuator count DMs for next-generation AO is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.