Large-Area Blackbody Source (LABB)

The MBIR blackbody source is nearly identical to a source designed by personnel from the NIST and the Los Alamos National Laboratory (LANL) in support of a space-based optical sensor. The LANL blackbody source was calibrated in the LBIR facility at the NIST, using the LBIR absolute cryogenic radiometer. A special vacuum vessel was attached to the LBIR chamber to accommodate the blackbody source and to permit spatial uniformity measurements of the blackbody cavity. The MBIR blackbody has a temperature range of 180 K to 350 K. and its thermometers were calibrated at several temperatures within this range. The blackbody consists of a conical-cylindrical cavity, thick-film heater sections, an actively cooled shroud, and a cold aperture. The cavity has a diameter of 10.4 cm, with a 3.17:1 length-to-diameter ratio. It is constructed of aluminum alloy and is coated on the inside with Martin Enhanced Black. The calculated cavity emissivity is 0.999 in the 1 µm to 14 µm wavelength range when spectrally averaged over a 9.06 half-angle field-of-view. The cavity is divided into seven zones: three in the conical section, three in the cylindrical section and one at the exit aperture. Each zone has four platinum resistance thermometers (PRTs) around the outside circumference, equally spaced, and a thick-film heater attached over the outside surface. Each zone is then independently temperature controlled between 180 K and 350 K. The specially modified temperature controllers, which permit temperature averaging of the four PRT outputs, compute the average temperature within a given zone and control the temperature to the value required for that zone.