MRI: Development of an Improved Keck II Laser Launch Facility

California Association For Research In Astronomy, Kamuela HI

Investigators

Abstract

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.