MRI: Development of an Improved Keck II Laser Launch Facility

地面上的望远镜必须通过地球大气层的干扰来观察深空的物体。 当来自遥远物体的光穿过大气层时，由于风切变和大气层内温度和压力的变化，它会被湍流扩散，这有效地降低了地球望远镜的分辨率。这一困难可以在很大程度上通过采用激光导星（LGS）和自适应光学（AO）的相对较新的技术来克服，其中明亮的激光照亮目标物体附近的一片天空。激光的光被吸收，然后被高层大气中的钠原子重新发射，高层大气中的钠原子高于大部分干扰的低层大气。 然后，返回信号用于跟踪光的时间依赖性大气失真。自适应光学利用这些信息来快速调整望远镜仪器中的光学器件，以将图像恢复到（几乎）从大气层上方看到的图像。 W. M.几年前，凯克天文台开发并安装了第一个成功的LGS AO系统。凯克在AO的科学生产力方面领先于世界各地的天文学界。凯克望远镜的时间是非常宝贵的，任何提高其效率肯定会付出显着的回报，在科学回报。 今天正在进行的一些最令人兴奋的前沿天文研究来自凯克AO系统。 这对10米长的望远镜是目前使用的最大的反射镜。 由于光学系统的固有分辨率与其物镜的尺寸成比例，因此有必要使用自适应光学来接近衍射极限分辨率。现在，凯克LGS系统将进行重大升级，用一个新设计和改进的系统取代目前位于望远镜安装架一侧的激光发射投影仪，该系统将放置在望远镜光轴上。 这种升级将减少波前传感系统所看到的透视伸长。 新系统将显著提高分辨率、对比度和动态范围，并将使天体测量和测光性能提高两倍。

Telescopes on the ground must observe objects in deep space through the interference of the earth's atmosphere. As light from a distant object passes through the atmosphere it gets spread out by turbulence due to wind shear and changes in temperature and pressure within the atmospheric layers, which effectively diminishes the resolving power of earth-based telescopes. This difficulty can be overcome to a large extent by relatively new techniques employing Laser Guide Stars (LGS) and Adaptive Optics (AO) where a bright laser illuminates a patch of sky near the target object. The laser's light is absorbed and then re-emitted by sodium atoms in the upper atmosphere, above much of the interfering lower atmosphere. The return signal is then used to track the time-dependent atmospheric distortion of the light. Adaptive Optics uses this information to rapidly adjust optics in the telescope's instrumentation to restore the image to (nearly) what would be seen from above the atmosphere. The W.M. Keck Observatory developed and installed one of the first successful LGS AO systems at an astronomical observatory just a few years ago. Keck has led the world-wide astronomical community in AO in terms of scientific productivity by a significant margin. Keck telescope time is extremely valuable and any increase in its effectiveness will certainly pay significant payoffs in science return. Some of the most exciting front-line astronomical research being done today comes from the Keck AO system. The twin 10-meter telescopes house the largest reflecting telescope mirrors in use today. Because the native resolution of an optical system scales with the size of its objective, it is necessary to use adaptive optics to approach diffraction-limited resolution. Now the Keck LGS system will undergo a significant upgrade, replacing a laser launch projector currently on the side of the telescope mount with a newly designed and improved system to be placed on the telescope optical axis. This upgrade will reduce the perspective elongation seen by the wavefront sensing system. The new system will have significantly improved resolution, contrast, and dynamic range and will lead to improved astrometric and photometric performance by up to a factor of two.