METIS: final design of the Imager sub-system

Abstract

METIS, the Mid-infrared Imager and Spectrograph for the Extremely Large Telescope (ELT), is one of the three firstgeneration science instruments and about to complete its final design phase [1]. The Imager sub-system provides diffraction-limited imaging capabilities and low-resolution grism-spectroscopy in two channels: one covers the atmospheric L&M bands with a field of view of 11x11 arcsec, and the second covers the N band, with a field of view of 14x14 arcsec.Both channels have a common collimator and a dichroic beam splitter dividing the light into two dedicated cameras and the corresponding detectors. In addition, the Imager provides a precise pupil re-imaging implementation allowing the positioning of high-contrast imaging masks for coronagraphic applications. The two channels are equipped with a HAWAII-2RG detector for LM-band and a GeoSnap detector for the N-band.We present the final optical design of the Imager in a summary, as well as the cryo-mechanical concept. The mechanical design gives an overview of the general design aspects and the analyses that demonstrate the approach how to deal with demanding stability and alignment requirements for high-contrast imaging. It further focuses on the design of individual units as e.g., on the GeoSnap detector mount and on the pupil re-imager. In addition, we exemplarily outline some of the key alignment and verification tasks, essential to guarantee the performance of the Imager.

Status update on the development of METIS, the mid-infrared ELT imager and spectrograph

“…The imager covers the wavelength range from L to N band (approximately 3 -13 µm). For optimal performance, this wavelength range is split into two channels, which are equipped with two different science detectors [23]. The imager has a collimator, that is common to both channels, and two camera optics optimized for the field of view (Figure 1), defined by the science detectors and the required sampling (5.5 marcsec pixels at L/M band and 6.8 marcsec pixels at Nband).…”