可见光自适应光学的实现技术：麦哲伦自适应二次VisAO相机
Enabling Technologies for Visible Adaptive Optics: The Magellan Adaptive Secondary VisAO Camera
摘要：
从一开始，衍射受限的地面自适应光学（AO）成像就被限制在近红外（λ > 1微米）和更长的波长。可见光AO（λ < 1微米）已被证明是困难的，因为较短的波长需要在非常短的空间和时间尺度上进行波前校正。光瞳必须非常精细地采样，这需要密集的致动器间距和具有大动态范围的精细波前采样。此外，大气色散在可见光区比在近红外区更为显著。在宽可见光波段成像需要非常好的大气色散校正器（ADC）。即使有这些技术，我们的AO模拟使用CAOS代码，结合6.5米麦哲伦望远镜的光学和站点参数，展示了可见光（λ=0.7微米）Strehl在50毫秒的时间尺度上的大的时间变化。在几百毫秒，可见Strehl可以高达50%，低至10%。利用高斯特列尔周期需要非常快地读出CCD的能力，从而引入大量的读取噪声，或者使用可以阻挡低斯特列尔光的快速异步快门。我们的Magellan VisAO相机将使用先进的ADC，高速快门和我们的585执行器自适应次级，以在智利Las Campanas天文台的6.5米Magellan Clay望远镜上实现宽带（0.5-1.0微米）衍射限制图像。这将是迄今为止拍摄的最清晰和最深的可见光直接图像，分辨率为17 mas，比哈勃太空望远镜的衍射极限高出2.7倍。
英文摘要：
Since its beginnings, diffraction-limited ground-based adaptive optics (AO) imaging has been limited to wavelengths in the near IR (λ > 1 micron) and longer. Visible AO (λ < 1 micron) has proven to be difficult because shorter wavelengths require wavefront correction on very short spatial and temporal scales. The pupil must be sampled very finely, which requires dense actuator spacing and fine wavefront sampling with large dynamic range. In addition, atmospheric dispersion is much more significant in the visible than in the near-IR. Imaging over a broad visible band requires a very good Atmospheric Dispersion Corrector (ADC). Even with these technologies, our AO simulations using the CAOS code, combined with the optical and site parameters for the 6.5m Magellan telescope, demonstrate a large temporal variability of visible (λ=0.7 micron) Strehl on timescales of 50 ms. Over several hundred milliseconds, the visible Strehl can be as high at 50% and as low as 10%. Taking advantage of periods of high Strehl requires either the ability to read out the CCD very fast, thereby introducing significant amounts of read-noise, or the use of a fast asynchronous shutter that can block the low-Strehl light. Our Magellan VisAO camera will use an advanced ADC, a high-speed shutter, and our 585 actuator adaptive secondary to achieve broadband (0.5-1.0 micron) diffraction limited images on the 6.5m Magellan Clay telescope in Chile at Las Campanas Observatory. These will be the sharpest and deepest visible direct images taken to date with a resolution of 17 mas, a factor of 2.7 better than the diffraction limit of the Hubble Space Telescope.
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