Measurements of the LIGO pathfinder optics

A number of 150 mm apertures in 250 mm diameter plano-concave optics with departures from the nominal figure of a few nm were carefully tested using phase measuring interferometry and the data reduced using pixel based absolute testing techniques. We discuss some of the data reduction techniques used as well as the precautions taken to verify the accuracy of the results. After accounting for systematic errors introduced by interferometer imaging, we show that the surfaces can be characterized to a few nm peak-to-valley over spatial scales from the measurement aperture to a few mm.