Effective area measurement of apertures by optical method

Improvement of uncertainties in detector-based photometry and radiometry requires precise optical measurement of radiometric aperture area including diffraction from the aperture and scattering from its edge. This paper introduces a method for the aperture, of which measurement is based on radiant flux transmitted through the aperture. The radiant flux with a uniform irradiance distribution was made by superposition of Gaussian laser beams that is accomplished by translators. To calibrate the displacement of the translators, a heterodyne interferometer was used. For the aperture fabricated to 7 mm by a diamond turning machine, the area uncertainty was evaluated by considering repeatability, correction of translator displacement and efficiency variation of the integrating sphere. The result was compared with that obtained by a three-dimension profilometer.