Metrology of Large Cylinder Mirrors with a Scanning Optical Profiler

Abstract

It is often difficult to measure the figure of cylindrical optics and off-axis segments of conic sections by conventional interferometric techniques. Mirrors designed for extreme grazing incidence applications, e.g., x-ray astronomy or synchrotron radiation beamlines, usually present a highly-foreshortened aperture to a conventional optical test system, making it nearly impossible to interpret the resultant interference pattern. As an end user of a large number of cylindrical aspheric optics, all with different surface figure parameters, and manufactured by a large number of different vendors, the National Synchrotron Light Source at Brookhaven National Laboratory has found it necessary to develop other techniques for characterizing the surface figure of such optical components. In order to be sufficiently versatile to handle a large variety of optical surfaces, we have developed a scanning interferometer system1 based upon the pencil beam interferometer principle2 that is capable of traversing a one meter distance, with a minimum step size dependent upon the laser beam diameter, which is currently one millimeter.