The METIS imaging-spectrometer for the ESO extremely large telescope

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Mechanical and optical studies for an extremely large telescope mid-infrared instrument

Publication . Boné, André Miguel Baptista; Amorim, António; Garcia, Paulo

Extremely Large Telescopes are considered worldwide as one of the highest priorities in ground-based astronomy, since they have the potential to vastly advance astrophysical knowledge. ESO is building its own Extremely Large optical and infrared Telescope, the ELT. This new telescope will have a 39m main mirror and will be the largest optical telescope in the world, able to work at the diffraction limit. METIS, one of the first light instruments of the ELT, has powerful imaging and spectrographic capabilities on the thermal wavelengths. It will allow the investigation of key properties of a wide range of celestial objects. METIS is an extremely complex instrument, weighing almost 11t, and requiring high positioning and steering precisions. Here I present the ELT’s METIS’ Warm Support Structure. It consists of a seven leg elevation platform, an hexapod capable of providing METIS with sub-millimetre and arcsecond positioning and steering resolutions, and an access platform where personnel can perform in-situ maintenance activities. The structure weighs less than 5 t and is capable of surviving earthquake conditions with accelerations up to 5g. The current design is supported by FEM simulations in ANSYS®, and was approved for Phase C. I also study the impact of the Talbot effect on the optics of METIS. This near-field effect reimages high frequencies of the phase into the amplitude, having the potential to harm the High contrast imaging (HCI) modes of the instrument. I analyse the phase errors resulting from the surface form errors of optical elements and conclude that they have an impact of less than 3% on the amplitude considering the current specifications. Finally, I develop a way of replicating the behaviour of a vortex coronagraph with raytracing software. I use this to assess the straylight caused by this kind of coronagraphs.

2021-09Tese de doutoramento

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Fundação para a Ciência e a Tecnologia

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PD/BD/128266/2016