Journal
APPLIED OPTICS
Volume 47, Issue 30, Pages 5604-5615Publisher
OPTICAL SOC AMER
DOI: 10.1364/AO.47.005604
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Funding
- Defense Advanced Research Projects Agency Microanterma Arrays: Microsystems Technology (DARPA MIATA) Office
- National Science Foundation (NSF) [0501578]
- Directorate For Engineering
- Div Of Electrical, Commun & Cyber Sys [0501578] Funding Source: National Science Foundation
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This paper describes a calibrated broadband emitter for the millimeter-wave through terahertz frequency regime, called the aqueous blackbody calibration source. Due to its extremely high absorption, liquid water is chosen as the emitter on the basis of reciprocity. The water is constrained to a specific shape (an optical trap geometry) in an expanded polystyrene (EPS) container and maintained at a selected, uniform temperature. Uncertainty in the selected radiometric temperature due to the undesirable reflectance present at a water interface is minimized by the trap geometry, ensuring that radiation incident on the entrance aperture encounters a pair of s and a pair of p reflections at 45 degrees. For water reflectance R. of 40% at 45 degrees in W-band, this implies a theoretical effective aperture emissivity of (1 - (RwsRwp2)-R-2) > 98.8%. From W-band to 450 GHz, the maximum radiometric temperature uncertainty is +/- 0.40 K, independent of water temperature. Uncertainty from 450 GHz to 1 THz is increased due to EPS scattering and absorption, resulting in a maximum uncertainty of -3 K at I THz.
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