A non-contact measurement of radiometric apertures with an optical microtopography sensor

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Abstract
In precision optical radiometry one of the accuracy limiting factors is the measurement uncertainty for the area determination of the beam limiting apertures. A technique for measuring these areas very precisely has been developed. In order to avoid damaging the fragile edges of the apertures a noncontact method for their detection is applied. A focused laser beam is used to measure the height profile of the aperture near its edge with a high lateral resolution. The height profile observed makes it possible to calculate the mean diameter of the aperture with an uncertainty of 0.4 mu m (68.3% confidence limits). The experimental set-up and the measurement technique are explained in detail. Representative results are shown and an estimation of the individual contributions to the uncertainty is given.