Ge immersed grating manufacturing and optical verification for the METIS high-resolution spectrograph

Tibor Agócs; Eddy Elswijk; Daan Zaalberg; Jan Rinze Peterzon; Niels Tromp; Ivan Lloro; Jeffrey Lynn; Ramon Navarro; Takashi Sukegawa; Yukinobu Okura; Stephen Todd; Alistair Glasse; Philip Parr-Burman; Bernhard Brandl; Felix Bettonvil

doi:10.1117/12.2562411

13 December 2020 Ge immersed grating manufacturing and optical verification for the METIS high-resolution spectrograph

Tibor Agócs, Eddy Elswijk, Daan Zaalberg, Jan Rinze Peterzon, Niels Tromp, Ivan Lloro, Jeffrey Lynn, Ramon Navarro, Takashi Sukegawa, Yukinobu Okura, Stephen Todd, Alistair Glasse, Philip Parr-Burman, Bernhard Brandl, Felix Bettonvil

Author Affiliations +

Proceedings Volume 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV; 114511G (2020) https://doi.org/10.1117/12.2562411
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Abstract

We present the manufacturing and optical verification of the germanium immersed grating for the L/M band high resolution spectrograph (LMS). The LMS is one of the science subsystems of the Mid-infrared ELT Imager and Spectrograph, METIS. The immersed grating has very demanding requirement specifications: <100 nm RMS transmitted Wave Front Error (WFE) after double pass, and >70% peak throughput in all orders within the 2.9-5.3 μm wavelength range over the pupil. The grating has a period of 18.2 μm, a sawtooth groove profile with 89.6 degrees apex angle and a grating area of 150mm x 60mm. The germanium immersed grating was produced by Canon’s high precision mechanical cutting technology. We present the interferometric tests that were performed in order to verify WFE and two different measurements (based on cascade laser and Fourier Transform Spectrometer, respectively) for throughput verification.

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Tibor Agócs, Eddy Elswijk, Daan Zaalberg, Jan Rinze Peterzon, Niels Tromp, Ivan Lloro, Jeffrey Lynn, Ramon Navarro, Takashi Sukegawa, Yukinobu Okura, Stephen Todd, Alistair Glasse, Philip Parr-Burman, Bernhard Brandl, and Felix Bettonvil "Ge immersed grating manufacturing and optical verification for the METIS high-resolution spectrograph", Proc. SPIE 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV, 114511G (13 December 2020); https://doi.org/10.1117/12.2562411

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