A new optical method for high-accuracy determination of aperture area

Abstract

We have developed a direct optical method for aperture area measurement, based on constant, known irradiance over the aperture. The method is described and results of test measurements are given, including wavelength dependence of the effective aperture area. Systematic uncertainty components are studied experimentally to reach a relative uncertainty of 10 -4 for aperture sizes down to 3 mm in diameter. The most important advantages of the direct optical method are that it does not require any reference aperture, it can be applied to apertures of any shape, and the calibration setup is similar to the actual use of the apertures in filter radiometers.

Optical aperture area determination for accurate illuminance and luminous efficacy measurements of LED lamps

“…The laser scanning method is described in detail in [18][19][20]. Therefore, only a brief introduction is given here.…”

“…(6) is presented in [19] for a relaxed requirement of the beam grid dimensions and general beam shape, not limited to a perfect Gaussian. For an aperture considerably smaller than the laser beam lattice, the aperture area can now be obtained by combining Eqs.…”

“…Several methods for determining the area of an aperture have been developed, which utilize either mechanical contact [16,17] or optical techniques [18][19][20][21][22][23][24][25]. In addition, a spatially uniform irradiance source can be used to compare the area of two apertures [16,26,27].…”

“…While most methods measure the diameter of a round aperture, some measure the area directly and can be used to measure irregular apertures. Lassila et al developed such an optical method for direct determination of aperture area [18][19][20], in which a two-dimensional superposition of equally spaced Gaussian laser beams is used to form a uniform irradiance distribution. In practice, this is accomplished by having an intensity-stabilized laser beam and scanning the aperture in front of the laser beam.…”

“…The method has been validated by comparing the measured area of apertures of different sizes to the area determined using mechanical contact methods [18][19][20].…”