METIS is a sophisticated mid-infrared imager and spectrograph covering wavelengths from 2.9 to 13.5 μm (astronomical L, M, and N bands), stands as one of the three primary science instruments at the Extremely Large Telescope (ELT). METIS will provide diffraction-limited imaging, coronagraphy, high-resolution integral field spectroscopy, and low/medium-resolution slit spectroscopy. Within the international METIS consortium, the University of Cologne is responsible for designing, manufacturing, integrating, and testing the Warm Calibration Unit (WCU). Among the other calibration functionalities, the WCU also facilitates alignment checks during Assembly, Integration, and Verification (AIT & AIV) through a visible light channel utilizing a CMOS camera, which can capture images of internal focal planes, pupil planes of the WCU, and various METIS sub-systems. This paper details the final optical design, preliminary opto-mechanical design, and analysis of alignment optics in the WCU. A laboratory test setup has been discussed, showcasing the estimation of SNR for the AIV mode of the WCU using an off-the-shelf CMOS camera and interating sphere. This paper also introduces the novel design concept of aluminum spherical mirrors employed in the main optical train of the WCU. We also present a brief overview of alignment verification procedures of the offner relay optics of the WCU sub-system. Furthermore, a detailed overview of the thermal analysis of the whole WCU will be discussed, which ensures the temperature difference between the WCU and the ELT dome will be within specified limits.
ProtoPol is a medium-resolution echelle spectro-polarimeter initially conceived as a prototype instrument of the currently under development M-FOSC-EP (Mt. Abu Faint Object Spectrograph and Camera-Echelle Polarimeter) instrument - a two-channel multimode instrument which is currently being designed for PRL 1.2m and 2.5m telescopes at Mt. Abu. Though ProtoPol was initially conceived to evaluate the development methodology of M-FOSC-EP with commercially available off-the-shelf components, it was later elevated to the level of a full-fledged back-end instrument for PRL telescopes. ProtoPol was designed on the concept of echelle and cross-disperser gratings to record the cross-dispersed spectra in the wavelength range from 390 to 940 nm with a resolution (λ/δλ) in the range of 7000-8000. ProtoPol has been successfully developed and commissioned on PRL 1.2m and 2.5m telescopes since December 2023, and a variety of observations are being carried out for instrument characterization and scientific purposes. The design and development methodology of ProtoPol with complete off-the-shelf components offers a cost-effective way to develop spectro-polarimeters with such resolutions for small aperture (2-3m) telescopes around the world with a shorter development period.
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.
Mt. Abu Faint Object Spectrograph and Camera-Echelle Polarimeter (M-FOSC-EP) is a two-channel multimode instrument currently under design for the upcoming PRL 2.5m telescope at Mt. Abu, India. M-FOSC-EP would provide capabilities of seeing limited imaging, low-resolution spectroscopy (R∼500-800), and high-resolution spectro-polarimetry (R∼15000) over the visible waveband. This design uses a common collimator optics, followed by a movable fold mirror to direct the incoming telescope beam into either of the low-resolution and spectropolarimetry modules, which are equipped with their separate detector system. As a precursor of M-FOSC-EP, a prototype spectro-polarimeter named ProtoPol is also being developed with commercially off-the-shelf optical components. ProtoPol could be used on existing 1.2m as well as on upcoming 2.5m PRL telescopes. Here we present the optical designs and performances of M-FOSC-EP and ProtoPol. In addition, the opto-mechanical design of ProtoPol has been presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.