- I. Physics Institute, University of Cologne, Zülpicher Str. 77, 50937 Cologne
- I. Physics Institute, University of Cologne, Zülpicher Str. 77, 50937 Cologne
- I. Physics Institute, University of Cologne, Zülpicher Str. 77, 50937 Cologne
The FYST telescope consists of two 6-meter mirrors. The mirrors are constructed from multiple panels, 77 on M1 and 69 on M2, with panel sizes of 67 cm x 75 cm and 70 cm x 71 cm respectively. The mirror panels are mounted on a carbon-fiber backup structure and aligned using 8 adjusters per panel. 3 adjusters determine the position of each mirror panel in the x-y plane, while 5 adjusters control the panel position in Z axis. These adjusters are used to precisely position the mirror panels, ensuring that the surface deviation between the designed and actual mirror surfaces is less than 10.7 micron (goal of 7 micron) over both mirrors. If the mirror shape deviates significantly from its ideal shape, it will affect the astronomical signal and instrument efficiency.
To achieve a surface precision at the 10-micron level, two independent systems will be deployed on the telescope: a microwave holography system and a laser metrology system. The holography system uses two heterodyne receivers to measure the telescope’s responses to a 300GHz source located 300 meters away from the telescope. The mirror shapes can then be reconstructed from the measured data. We have developed a new metrology system, including hardware and software, for the special FYST optics, capable of simultaneously measuring panel deviations across both mirrors.
The laser metrology system measures the positions of the mirror panels by reflecting a laser signal from 6 sources onto a retroreflectors on the mirror surfaces. The system is provided by the German company ETALON, with whom we work closely. Both systems generate a table of adjuster offsets, which are then applied to the mirror panels. Both systems can work independently and provide a dual approach to achieving this high level of mirror accuracy.