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. 2021 Oct 27;7:87. doi: 10.1038/s41378-021-00285-8

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© The Author(s) 2021, corrected publication 2022

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a Visible light image of the IR emitter during the burn-in of the Kanthal filament prior to mounting of the wavelength-selective lid. The IR emitter pads are electrically contacted using probes to perform a functional test. The suspended filament parts in the center of the emitting zone glow brighter than the filament near the guiding posts. b Diagram with multiple emission spectra from the IR emitter measured with the FTIR spectrometer. The relative intensity of the emitted IR radiation is plotted versus the wavelength in micrometer. The measured emission spectrum (black) using the step scan (SS) measurement mode shows good agreement with the calculated black body spectrum (BB) at 400 °C (black dashed line), considering an emissivity of 0.7 for Kanthal alloys. Additional measured emission spectra using constant driving currents are depicted with red, green, and blue lines, showing a significant discrepancy in the long-wavelength range beyond 6 μm. This is due to the background radiation emitted by the substrate and the package