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arXiv · 2606.24179

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

Benoit Sassolas·Matthieu Coulon·Christophe Michel·Laurent Pinard·Roland Bacon·Corentin Cudennec·Philippe Dierickx
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Abstract

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.

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Benoit Sassolas, Matthieu Coulon, Christophe Michel, Laurent Pinard, Roland Bacon, Corentin Cudennec, Philippe Dierickx. 2026-06-23. Widefield Spectroscopic Telescope (WST): coating strategy to achieve high optical throughput. https://arxiv.org/abs/2606.24179

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