Recent advances in measurement of radiometric aperture area using optical method at NIM

Aperture is widely used in optical instruments, for which the area is of importance especially for instruments measuring radiometric or photometric quantities. To measure the radiometric area of the aperture, an optical method using a power stabilized laser to scan the aperture was proposed and investigated by many metrology institutes worldwide. The National Institute of Metrology (NIM) of China has built an apparatus to measure the radiometric area aperture by using the optical method. The scheme of experimental setup and related issues are discussed in this work. Uncertainties are analyzed for an aperture with nominal 6mm diameter. Approaches for further improvements are also discussed.