Measurement of small apertures

The Low Background Infrared calibration facility at the National Institute of Standards and Technology (NIST) is developing an instrument to measure the relative areas of apertures with diameters ranging from 5 mm to 0.05 mm. NIST already has the capability of determining the absolute area of apertures with diameters larger than 0.35 mm. Our goal is to measure the area or radius of a 0.05 mm diameter aperture to a standard uncertainty of better than 0.1%. We report on the current status of this effort and plans for improvement. We are near the goal for apertures larger than 0.350 mm.