A NONCONTACT MEASUREMENT OF RADIOMETRIC APERTURES WITH AN OPTICAL MICROTOPOGRAPHY SENSOR

In precision optical radiometry one of the accuracy limiting factors is the measurement uncertainty for the area determination of the beam limiting apertures. Therefore a new technique for measuring these areas very precisely has been developed. In order to avoid damaging the fragile edges of the apertures a non-contact 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.