自适应光学中MEMS变形反射镜的行程饱和
Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics
摘要：
利用现有的自适应光学（AO）系统，最近从地面实现了对主序星周围太阳系外行星候选者的高对比度成像。推进这样的观测将是双子座行星成像仪的一项任务，双子座行星成像仪是一种即将推出的“极端”AO仪器。高阶“高音”和低阶“低音”可变形镜（DM）将提供>90%的Strehl校正，专门的日冕将抑制恒星通量，然后可以在“黑洞”区域成像任何行星。残留的波前误差将光线散射到DM控制的黑洞中，使得行星难以在噪声之上成像。在这方面至关重要的是，高密度高音扬声器（微机电系统（MEMS）DM）具有足够的行程以变形为大气湍流所需的形状。进行实验室实验以确定饱和的速率和情况，即中风不全。利用r_0=10- 15 cm的软件Kolmogorov湍流屏对1024个致动器的1.5 μ m冲程MEMS器件进行了经验测试。MEMS在孤立时约有4%的时间处于饱和状态。模拟低音扬声器DM，在5米的初级上具有约5-10个致动器，将MEMS饱和发生率降低到百分之几。虽然没有相邻的致动器在相对的位置饱和，中高空间频率的中风比预期的更频繁地饱和，这意味着通过影响函数的相关性是重要的。分析模型低估了中风的需求，所以实证研究是重要的。
英文摘要：
High-contrast imaging of extrasolar planet candidates around a main-sequence star has recently been realized from the ground using current adaptive optics (AO) systems. Advancing such observations will be a task for the Gemini Planet Imager, an upcoming "extreme" AO instrument. High-order "tweeter" and low-order "woofer" deformable mirrors (DMs) will supply a >90%-Strehl correction, a specialized coronagraph will suppress the stellar flux, and any planets can then be imaged in the "dark hole" region. Residual wavefront error scatters light into the DM-controlled dark hole, making planets difficult to image above the noise. It is crucial in this regard that the high-density tweeter, a micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform to the shapes required by atmospheric turbulence. Laboratory experiments were conducted to determine the rate and circumstance of saturation, i.e. stroke insufficiency. A 1024-actuator 1.5-um-stroke MEMS device was empirically tested with software Kolmogorov-turbulence screens of r_0=10-15cm. The MEMS when solitary suffered saturation ~4% of the time. Simulating a woofer DM with ~5-10 actuators across a 5-m primary mitigated MEMS saturation occurrence to a fraction of a percent. While no adjacent actuators were saturated at opposing positions, mid-to-high-spatial-frequency stroke did saturate more frequently than expected, implying that correlations through the influence functions are important. Analytical models underpredict the stroke requirements, so empirical studies are important.
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