03.02.2022
The Radiometric Calibration Spectral Source (RCSS) in the open vacuum chamber during calibration at PTB.
The James Webb Space Telescope (JWST) has arrived in January 2022 in its orbit foreseen around the Lagrange point L2, 1.5 million kilometres from Earth. The four scientific instruments of the JWST will now undergo final calibration in space before the first scientific results can be expected starting from summer 2022. For the NIRSpec (Near Infrared Spectrograph) instrument contributed by the European Space Agency ESA, PTB co-developed and characterised the calibration source for the lowest possible, on metrological level still detectable radiant powers several years ago. The Radiometric Calibration Spectral Source (RCSS) is a quasi-point source and imitates the focal ratio (f/20) and the hexagonal pupil shape of the JWST main mirror with special optics. For the calibration of the very low infrared radiation source in the spectral range from 0.7 µm to 1.55 µm, the RCSS was operated under vacuum at 90 K with a specially adapted single photon detector (Taubert et al., 2009). The RCSS was used for ground calibration prior to the flight to quantify the slit and diffraction losses in the spectroscopic operating modes of NIRSpec (Birkmann et al., 2014). The NIRSpec instrument should thus be able to spectrally resolve and analyse the very faint emissions from distant galaxies. Even the low absorptions of trace gases in the atmospheres of exoplanets can potentially be found and identified in this way.
Contact:
D. Taubert, 7.31, E-Mail: 
Dieter.Taubert(at)ptb.de
C. Monte, 7.32, E-Mail: Christian.Monte(at)ptb.de