The assembly and alignment of the 4MOST wide field corrector

Mark Cunningham; Peter Doel; David Brooks; Joar Brynnel; Roelof de Jong; Steffen Frey; Michael Schroeck; Miklos Gaebler; Daniel Sablowski; Michael Lehmitz; Greg Smith; Sam C. Barden

doi:10.1117/12.2629247

29 August 2022 The assembly and alignment of the 4MOST wide field corrector

Mark Cunningham, Peter Doel, David Brooks, Joar Brynnel, Roelof de Jong, Steffen Frey, Michael Schroeck, Miklos Gaebler, Daniel Sablowski, Michael Lehmitz, Greg Smith, Sam C. Barden

Author Affiliations +

Proceedings Volume 12184, Ground-based and Airborne Instrumentation for Astronomy IX; 121846V (2022) https://doi.org/10.1117/12.2629247
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a fibre-fed multi-object spectrograph for the VISTA telescope at the ESO Paranal Observatory in Chile. The goal of the 4MOST project is to create a general-purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square degree field of view and consists of an optical Wide-Field Corrector (WFC), a fibre positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of 6 lenses grouped into 4 elements, 2 of which are cemented doublets that act as an atmospheric dispersion corrector (ADC). The first lens element is 0.9m in diameter whilst the diameter of the other elements is 0.65m. For the instrument to meet its science goals, each lens needs to be aligned to ∼50µm – a major challenge. This is achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, a novel off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This paper details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC

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Mark Cunningham, Peter Doel, David Brooks, Joar Brynnel, Roelof de Jong, Steffen Frey, Michael Schroeck, Miklos Gaebler, Daniel Sablowski, Michael Lehmitz, Greg Smith, and Sam C. Barden "The assembly and alignment of the 4MOST wide field corrector", Proc. SPIE 12184, Ground-based and Airborne Instrumentation for Astronomy IX, 121846V (29 August 2022); https://doi.org/10.1117/12.2629247

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