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A New Deformable Mirror Architecture for Coronagraphic Instrumentation

机译：用于日冕仪器的新型可变形镜结构

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Coronagraphs are a promising solution for the next generation of exoplanet imaging instrumentation. While a coronagraph can have very good contrast and inner working angle performance, it is highly sensitive to optical aberrations. This necessitates a wavefront control system to correct aberrations within the telescope. The wavefront requirements and desired search area in a deformable mirror (DM) demand control of the electric field out to relatively high spatial frequencies. Conventional wisdom leads us to high stroke, high actuator density DMs that are capable of reaching these spatial frequencies on a single surface. Here we model a different architecture, where nearly every optical surface, powered or unpowered, is a controllable element. Rather than relying on one or two controllable surfaces for the success of the entire instrument the modeled instrument consists of a series of lower actuator count deformable mirrors to achieve the same result by leveraging the conjugate planes that exist in a coronagraphic instrument. To make such an instrument concept effective the imaging optics themselves must become precision deformable elements, akin to the deformable secondary mirrors at major telescope facilities. Such a DM does not exist commercially; all current DMs, while not necessarily incapable of carrying optical power, are manufactured with flat nominal surfaces. This simplifies control and manufacturing, but complicates their integration into an optical system because there is oftentimes a need to pack several into collimated space. Furthermore, high actuator count DMs cannot approximate low order shapes such as focus or tip-tilt without significant mid-spatial frequency residuals, which is not acceptable for a coronagraphic high-contrast imager. The ability to integrate the wavefront control system into the nominal coronagraphic optical train simplifies packaging, reduces cost and complexity, and increases optical throughput of any coronagraphic instrument. This adds redundancy, increases controllability of the complex aberrations, and mitigates both cost and risk associated with a single high-actuator count device that the entire instrument performance relies on. Here we simulate an optical system with a combination of controllable imaging optics both with and without a high order DM at the pupil. This example instrument is based loosely on the current DM technology being considered for the WFIRST CGI, and is merely an example of a larger trade study to be done to optimally balance actuator requirements, controllability, and wavefront quality. The relative performance of each configuration with regard to contrast, achievable bandwidth, and redundancy is discussed. The overall performance enhancements and risk associated with actuator failures on the assumed DM technology is also evaluated.
机译：日冕仪是下一代系外行星成像仪器的有前途的解决方案。虽然日冕仪可以具有非常好的对比度和内部工作角度性能，但它对光学像差非常敏感。这需要一个波前控制系统来校正望远镜内的像差。可变形反射镜（DM）中的波前要求和所需的搜索区域要求将电场控制到相对较高的空间频率。传统知识将我们引向高行程，高致动器密度DM，这些DM能够在单个表面上达到这些空间频率。在这里，我们对不同的架构进行建模，其中几乎每个通电或不通电的光学表面都是可控元素。建模的仪器不是依赖一个或两个可控的表面来使整个仪器成功使用，而是由一系列较低的执行器数量的可变形反射镜组成，可通过利用电晕仪中存在的共轭平面来达到相同的结果。为了使这种仪器概念有效，成像光学系统本身必须成为精密的可变形元件，类似于主要望远镜设施中的可变形辅助镜。这种DM在商业上不存在;当前的所有DM，虽然不一定能够承载光功率，但都是使用平坦的标称表面制造的。这简化了控制和制造，但是使它们集成到光学系统中变得复杂，因为通常需要将多个包装到准直空间中。此外，高执行器数量的DM无法在没有明显的中空间频率残留的情况下近似低阶形状（例如聚焦或倾斜），这对于日冕式高对比度成像仪是不可接受的。将波前控制系统集成到标称冠状光学光学系统中的能力简化了包装，降低了成本和复杂性，并增加了任何冠状光学仪器的光通量。这增加了冗余，增加了复杂像差的可控性，并降低了整个仪器性能所依赖的单个高致动器计数设备的成本和风险。在这里，我们模拟了一个光学系统，该系统结合了可控成像光学器件，在瞳孔处有或没有高阶DM。该示例仪器大致基于WFIRST CGI所考虑的当前DM技术，并且仅是为了最大程度地平衡执行器要求，可控制性和波前质量而进行的一项大型贸易研究的示例。讨论了每种配置在对比度，可达到的带宽和冗余方面的相对性能。还评估了假定的DM技术上的整体性能增强和与执行器故障相关的风险。

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