Automatic reflectivity map measurement of high power CO₂ laser optics

An automatic system has been developed for the measurement of the reflectivity map of large-sized optics used in high-power CO₂ laser devices. The CO₂ laser beam is devided into two. One beam is reflected by the sample optic and the other is used as a reference. Both beams are chopped at separate frequencies and their polarizations are perpendicular. The relative reflectivity is obtained through the analysis of the two beam signals from the simultaneous detection. The normal of any measuring point is adjusted automatically by four-axes control, to coincide with the axis of the optical system. The reflectivity map of an optic with a diameter of up to 150 mm has been obtained. The accuracy of the reflectivity is confirmed to be within 0.5% of the measured value.