Method for measuring the area of radiometric apertures using the ratio of Gaussian beams

I propose and demonstrate a method for determining the area of radiometric apertures using the power ratio between Gaussian beams. The result relies on measuring the power of an optical beam of known radius with and without the radiometric aperture, this with area smaller than the beam spot. The impact of the characterization of the laser beam and of the radiometric measurements on the area estimation is discussed and a 3-mm in-diameter sample is measured for validation. The contactless method is fast and simple and results in a relative uncertainty of 0.12% for the sample studied.