Cryogenic Far-Infrared Laser Absorptivity Measurements of the Herschel Space Observatory Telescope Mirror Coatings
NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
Pagination or Media Count:
Far-infrared laser calorimetry was used to measure the absorptivity, and thus the emissivity, of aluminum-coated silicon carbide mirror samples produced during the coating qualification run of the Herschel Space Observatory telescope to be launched by the European Space Agency in 2007. The samples were measured at 77 K to simulate the operating temperature of the telescope in its planned orbit about the second Lagrangian point, L2, of the Earth Sun system. Together, the telescopes equilibrium temperature in space and the emissivity of the mirror surfaces will determine the far-infrared submillimeter background and thus the sensitivity of two of the three astronomical instruments aboard the observatory if stray-light levels can be kept low relative to the mirror emission. Absorptivities of both clean and dust-contaminated samples were measured at 70, 118, 184, and 496 micrometers. Theoretical fits to the data predict absorptivities of 0.2-0.4 for the clean sample and 0.2-0.8 for the dusty sample, over the spectral range of the Herschel Space Observatory instruments.
- Coatings, Colorants and Finishes
- Optical Detection and Detectors