LINC-NIRVANA is an instrument combining the two 8.4 m telescopes of the Large Binocular Telescope (LBT) coherently, in order to achieve the optical resolution of the 23 meter baseline. For this interferometric instrument concept, the common beam combination requires diffraction limited optical performance. The optics, realized as a Cassegrain telescope design, consists of aluminum mirrors, designed and manufactured to fulfill the challenging specifications required for interferometric imaging. Due to the science wavelength range from 1 μm to 2.4 μm, covering the J, H and K band of the atmosphere, the complete beam combiner including the optics is operated in cryogenic environment at 60 Kelvin. Here, we demonstrate the verification of the optical performance at this temperature for classical in-coherent and coherent illumination. We outline the test setup and present the achieved results of wavefront error for the individual beams and fringe contrast for the interferometric point spread function. This paper continues the already presented integration of the interferometric camera with the focus on the performance of the cryogenic optics.

Date Published: 8 July 2014
PDF: 13 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 91474B (8 July 2014); doi: 10.1117/12.2057473

Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)