New spectro-imager designs for MOEMS-based instruments in Earth and Universe observation

Vachey, Mathieu; Zamkotsian, Frédéric; Costes, Vincent; Benard, Hervé; Liotard, Arnaud; Tetaz, Nicolas

doi:10.1117/12.2569670

Cited by 1 publication

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“…A 3-mirror solution for both imaging and spectrograph arms has been designed, using only aspheric surfaces thus allowing for easier alignment and tolerancing. 13 This paper describes the design, the realization and the characterization of a new type of non-planar reflective gratings, key components for future high throughput spectrographs in space missions.…”

Section: Virtual Conference 30 March-2 April 2021mentioning

confidence: 99%

Blazed gratings on convex substrates for high throughput spectrographs for Earth and Universe observation

Zamkotsian

Zhurminsky

Lanzoni

et al. 2021

International Conference on Space Optics — ICSO 2020

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In next generation space instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, our requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the Telescopio Nazionale Galileo (TNG) and called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 -800 nm. Such gratings have been fabricated and coated with a silver-based layer, with a final 7° blaze angle over the whole surface. Efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. Detailed mapping of the blazed grating showed a very good period uniformity with up to 0.5% deviation. Grating depth and blaze angle have higher deviation, up to 7%. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Preliminary straylight measurement has been done and shows a lowest straylight level below 10 -2 sr -1 between the diffraction orders. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions.

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Section: Virtual Conference 30 March-2 April 2021mentioning

confidence: 99%