We present the as-manufactured design of the cryostat of the Mid-infrared ELT Imager and Spectrograph (METIS) instrument to be operated at ESO's Extremely Large Telescope (ELT). The cryostat provides the cold optics of the instrument with the required cryo-vacuum environment. The radiation shields of the cryostat are cooled with liquid nitrogen and the cold optics is cooled via pulse-tube coolers down to temperatures between 35 K and 70 K. The cold-warm interface is provided with G10 blades that build together with the top part of the cryostat vessel the structural interface to the cold optics, the warm support structure, and the warm calibration source. The cryostat design is now finalized with most of the parts already produced and final integration on-going. We present in this paper the final design as manufactured, the key design considerations, and highlights from the integration phase.

METIS is one of the first-generation instruments currently in development for the Extremely Large Telescope (ELT). As one of the partners in the project consortium, the team at University of Cologne is responsible for the development of the Warm Calibration Unit (WCU) subsystem. This subsystem is designed to deliver a selection of broadband and single wavelength sources for the calibration of the METIS instrument along with pupil/focal plane imaging optics serving as feedback for the internal alignment of the subsystems of METIS during the integration phase foreseen in Leiden. After the satisfactory Final Design Review (FDR) towards the end of 2022, the development of the WCU subsystem is currently in the manufacturing/procurement phase along with the integration of sub-assemblies. We provide an overview of the development of the WCU subsystem at this phase of the project including the progress on the manufacturing of custom components and the details on the compliance with the design principles with a primary focus on the mechanical aspects. These components include as an example: (1) a lightweight optical bench made of carbon-fiber reinforced polymer (CFRP) and with dimensions of roughly 2.5mx3m and a thickness of 20cm, satisfying compliancy both with high loads and tight tolerances (on the level of several tens of microns), (2) custom-designed six adjustable supporting links responsible for carrying the subsystem (roughly 1 tons) and its alignment to METIS focal/pupil planes within desired accuracies 50 microns with the help of laser sensors, (3) kinematic optical Aluminum mounts with a thermal invariant design (i.e. positioning of the optics are not affected by temperature). In the light of the progress, we discuss further the perspectives and the planning towards the full integration and testing of the full subsystem, foreseen to start within the second quarter of 2025.

Hi-5 is the L'-band (3.5-4.0 μm) high-contrast imager of Asgard, an instrument suite in preparation for the visitor focus of the VLTI. The system is optimized for high-contrast and high-sensitivity imaging within the diffraction limit of a single UT/AT telescope. It is designed as a double-Bracewell nulling instrument producing spectrally-dispersed (R=20, 400, or 2000) complementary nulling outputs and simultaneous photometric outputs for self-calibration purposes. In this paper, we present an update of the project with a particular focus on the overall architecture, opto-mechanical design of the warm and cold optics, injection system, and development of the photonic beam combiner. The key science projects are to survey (i) nearby young planetary systems near the snow line, where most giant planets are expected to be formed, and (2) nearby main sequence stars near the habitable zone where exozodiacal dust that may hinder the detection of Earth-like planets. We present an update of the expected instrumental performance based on full end-to-end simulations using the new GRAVITY+ specifications of the VLTI and the latest planet formation models.

The METIS instrument (Mid-infrared ELT Imager and Spectrograph) is one of the three first-light instruments for the ELT.(1,2) It will work in the mid-infrared with a set of four different focal planes, grouped in three different subsystems: the imager (IMG) and the spectrograph (LMS) are the two scientific focal planes, and the last one, SCAO, is the dedicated adaptive optics system. In total, this instrument requires five H2RG detectors (5.3 mu m cutoff), one SAPHIRA detector (2.5 mu m) and one GEOSNAP (13.5 mu m). All of these detectors will be controlled by the New General Controller, second generation (NGCII). These three separate subsystems require specific tests and development : the IMG needs a fast readout for both N and LM channels, the LMS requires a mosaic of four detectors and SCAO works with one single detector operated fast for AO corrections. In this paper, we will present the challenges for the development of the detector systems of the three detector subunits in METIS. This includes the design, tests and preparations for the AIT/AIV phases that each subsystem has to go through. First, we describe the detector-specifics of all the instruments. In a second part, we go over the design challenges for these detector subunits. In the end, we will report on the current testing.

ESO's Very Large Telescope Interferometer has a history of record-breaking discoveries in astrophysics and significant advances in instrumentation. The next leap forward is its new visitor instrument, called Asgard. It comprises four natively collaborating instruments: HEIMDALLR, an instrument performing both fringe tracking and stellar interferometry simultaneously with the same optics, operating in the K band; Baldr, a Strehl optimizer in the H band; BIFROST, a spectroscopic combiner to study the formation processes and properties of stellar and planetary systems in the Y-J-H bands; and NOTT, a nulling interferometer dedicated to imaging nearby young planetary systems in the L band. The suite is in its integration phase in Europe and should be shipped to Paranal in 2025. In this article, we present details of the alignment and calibration unit, the observing modes, the integration plan, the software architecture, and the roadmap to completion of the project.

We present the final design of the cryostat of the Mid-infrared ELT Imager and Spectrograph (METIS) instrument to be operated at ESO's Extremely Large Telescope (ELT). The cryostat provides the cold optics of the instrument with the required cryo-vacuum environment. The radiation shields of the cryostat are cooled with liquid nitrogen and the cold optics is cooled via pulse-tube coolers down to temperatures between 35 K and 70K. The cold-warm interface is provided with G10 blades that build together with the top part of the cryostat vessel the structural interface to the cold optics, the warm support structure and the warm calibration source. The cryostat development is now complete and the instrument Final Design Review is scheduled for November 2022. We present in this paper the final design status, the key design considerations and the cooling concept.

METIS, the Mid-infrared E-ELT Imager and Spectrometer, is being designed for the Extremely Large Telescope (ELT) and is currently expected to arrive at the telescope early 2028. As part of the design of the instrument, we are developing the Assembly, Integration and Verification strategy for METIS. Although the sub-systems will be largely qualified at their respective institutes, only once all components come together at system level will it be possible to verify all the interfaces, full system thermal characteristics and full instrument performance. Although one of the smaller instruments for the ELT, the fully integrated METIS will still be more than 7 meters high, with a footprint in excess of 15 square meters and a weight of the order of 10 tons. This paper describes the system level assembly, integration and verification of METIS, both in Europe as well as once delivered to the telescope.