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

Conference paper (2020)

Authors

Tibor Agocs Netherlands Institute for Radio Astronomy (ASTRON)
Eddy Elswijk Netherlands Institute for Radio Astronomy (ASTRON)
Daan Zaalberg Netherlands Institute for Radio Astronomy (ASTRON)
Jan Rinze Peterzon Netherlands Institute for Radio Astronomy (ASTRON)
Niels Tromp Netherlands Institute for Radio Astronomy (ASTRON)
Ivan Lloro Netherlands Institute for Radio Astronomy (ASTRON)
Jeffrey Lynn Netherlands Institute for Radio Astronomy (ASTRON)
Ramon Navarro Netherlands Institute for Radio Astronomy (ASTRON)
B.R. Brandl Universiteit Leiden, Astrodynamics & Space Missions - Aerospace Engineering
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Research Group
Astrodynamics & Space Missions (Aerospace Engineering) (TU Delft)
Verification Manufacturing Germanium Throughput Mid-infrared METIS Immersed grating Wavefront error
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Published Date

2020

Language

English

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Faculty

Aerospace Engineering

Department

Space Engineering

Research Group

Astrodynamics & Space Missions

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.