arXiv subjects

Corentin Cudennec

Publications and source records attributed to Corentin Cudennec.

6 recordsLinked to original sources

arXiv2026

Design evolution for the Wide-field Spectroscopic Telescope

WST is proposed as the next large ESO project to follow ELT, combining Multi-Object Spectroscopy and Integral Field Spectroscopy. Each mode offers order-of-magnitude gains over current systems, and each also presents unprecedented design challenges, both separately and in combination. For large MOS systems, both science performance and spectrograph costs vary steeply with the delivered image quality, so exceptional delivered image quality is paramount. But the 12m aperture and 2 degree field give WST an etendue larger than Rubin, larger that LAMOST, and larger than all other existing MOS telescopes combined; while the IFS, segmented primary and windy site all add additional constraints. Hence finding designs with good image quality is challenging. Eventually, 3-lens Forward Cassegrain designs with loss-less ADC were developed in variants mostly differentiated by M2 diameter. The lowest technical risk design, with the smallest M2, was selected as the baseline, with wind-shake control a primary driver. However, other designs have better as-designed image quality, and their perceived risks may diminish as the system design and underlying technologies mature. For IFS mode, delivered image quality is just as crucial, but this is achieved through additional optics and NGS GLAO over the 3'x3' field. The challenges come from (a) transferring the F/3.4 Forward Cassegrain focus to a fixed focus under the telescope; (b) a requirement that the 3'x3' field be selectable from a 13' diameter FoV without repointing the telescope; (c) including a suitably conjugated mirror for GLAO correction; (d) doing all this with minimised vignetting and surface count. Various designs were explored; the baseline design has a field-selecting pick-off at telescope focus, combined with large reimaging optics at Nasmyth, giving an F/28.5 fixed IFS focus.

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arXiv2026

WST, the Wide-field Spectroscopic Telescope: dispersing elements

The Wide-field Spectroscopic Telescope (WST) is a proposed 12-m class facility entirely dedicated to spectroscopic surveys, combining a high-multiplex multi-object spectrograph operating at low (MOS-LR) and high (MOS-HR) spectral resolution with a giant panoramic integral-field spectrograph (IFS), all three operating in parallel. Diffraction gratings are the key dispersing elements of all three instruments and, given the very large number and size of the units required, drive critical trade-offs in throughput, feasibility and production cost. This paper reviews the two grating technologies under consideration for WST, Volume Phase Holographic Gratings (VPHG) and binary (lithographic, surface-relief) gratings, summarizing their working principles and the parameters that control their diffraction efficiency. We then present the current baseline grating parameters and vendor results for each instrument: low-dispersion, VPHGs for the IFS; a four-arm GRISM layout for MOS-LR; and two competing high-resolution disperser architectures (8M16D and 16M4D) for MOS-HR, where binary gratings show a promising path to diffraction efficiencies beyond what is achievable with VPHGs. We conclude with the main open challenges, chiefly the mass production of hundreds of grating units within cost and schedule and the next steps foreseen to consolidate the disperser baseline for WST.

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arXiv2026

WST, the wide-field spectroscopic telescope: progress on the design of the instruments

WST, the Wide-field Spectroscopic Telescope is a proposed new facility that will provide a transformational gain in spectroscopic survey capability over existing facilities. The WST is a 12 metre class telescope equipped with instrumentation to provide simultaneous observations in both multiple-object spectroscopy and integral field spectroscopy modes. This paper will describe the status of the instruments being designed for the WST, the fibre positioner module, the low and high-resolution multiple object spectrographs, the integral field spectrograph, disperser technology, sustainable detector and cryostat technology, and the calibration system. An overview of the overall layout of the instruments within the WST facility will be provided.

astro-ph.IM↗

arXiv2026

Widefield Spectroscopic Telescope (WST): coating strategy to achieve high optical throughput

The Wide-field Spectroscopic Telescope (WST) is a 12-m class facility designed for simultaneous wide-field multi-object and integral-field spectroscopy across 370-1600 nm, targeting a throughput above 83% its wide-field focus and 76% at its integral field one. Its 13 mirrors and 5 lenses require optimized coatings balancing feasibility, operational needs, and long-term durability. Large mirrors (>2 m) may use enhanced metallic coatings, such as the protected-silver solution from the Vera C. Rubin Observatory, achieving over 90% reflectivity in UV and above 99% in NIR. Smaller mirrors would use Nb2O5/SiO2 dielectric stacks, offering 99% reflectivity, tunable spectral response, and excellent stability. Coating the large lenses (up to 1.6 m) is challenging due to the ultra-broadband range, traditional multilayer antireflective coatings show limitations from manufacturing and incidence-angle effects. Graded-index AR coatings are being explored for superior performance across broad wavelengths and angles.

astro-ph.IM↗

arXiv2026

WST -- Wide-field Spectroscopic Telescope: The Next Leap in Wide-field Spectroscopy

The Wide-field Spectroscopic Telescope (WST) is a concept for a dedicated 12-m spectroscopic survey facility designed to address some of the most important questions in astrophysics in the 2040s. The WST will provide unprecedented spectroscopic survey capabilities by operating simultaneously over a 2-degree diameter field of view with 54 low-resolution spectrographs fed by 30,000 fibres, 8-16 high-resolution spectrographs fed by 2,000 fibres, and a large panoramic low-resolution integral-field spectrograph. Supported by Horizon Europe, the concept study has refined the science cases, facility architecture, operations model, sustainability strategy, and technology roadmap. The resulting reference design demonstrates that the WST is both scientifically transformative and technically feasible, while identifying the developments required to mitigate the remaining risks. The WST is designed as an ESO flagship facility for the post-ELT construction era and a key spectroscopic complement to the major imaging, time-domain, and multi-messenger facilities of the coming decades.

astro-ph.IM↗

arXiv2026

IFS spectrograph designs for the Wide-field Spectroscopic Telescope: Architecture and performance gains from curved sensors

The Wide-field Spectroscopic Telescope (WST) is a proposed 12-meter segmented facility optimized for seeing limited observations in the visible and designed to operate both a high-multiplex multi-object spectrograph and a panoramic integral field spectrograph (IFS). The WST IFS concept builds on instruments such as MUSE at the VLT (Very Large Telescope), using field splitters and image slicers to reformat a large field into pseudo-slits feeding spectrographs with two optimized spectral channels. This paper presents the spectrograph architecture developed for the WST IFS, aiming to achieve high through put and image quality over a wide wavelength range in a cost-effective manner. We investigate the use of curved detectors as a means to simplify the spectrograph layout, reduce aberrations, and potentially improve efficiency. This study establishes a promising baseline for the IFS spectrographs and assesses the benefits of incorporating curved sensors that can guide the development of future large-scale integral field spectrographs.

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