The optomechanical design of the LTAO WFS for the Giant Magellan Telescope

The Giant Magellan Telescope presents a unique astronomical facility with seven 8.4 m diameter primary mirrors matched by seven adaptive secondary mirrors (ASM). The ASMs will be controlled by several Adaptive Optics systems; one of them is the Laser Tomography Adaptive Optics (LTAO) system. A key component in any design of a LTAO system is the Laser Tomographic Wavefront Sensor (LTWS). The LTWS Assembly consists of six optically equal 60×60 Shack-Hartmann WFS aligned to the six Laser Guide Stars (LGS). Changing telescope elevation and changes in the mean altitude of the sodium layer result in a varying back focal distance and F-number. Therefore, very accurate focus compensation and pupil size adjustment, combined with very high requirements for pupil stability and optical performance, are the main challenges for opto-mechanical design of the LTAO WFS Assembly. We are presenting a compact solution developed during the LTAO preliminary design phase. In our design, the six LGS wavefront sensors use the same focus and zoom stage. Besides the presentation of the optical performance, we will show the results of the tolerancing, the alignment concept and the mechanical realization.