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Penta-Prism Long Trace Profiler (PPLTP) for measurement of grazing incidence space optics

The long trace profiler (LTP) is in use at a number of locations throughout the world for the measurement of the figure and mid-frequency roughness of x-ray mirrors. The standard configuration requires that the surface tested lie in a horizontal plane as the optical head is scanned along a horizontal line. For applications where gravity-induced sag of the surface cannot be tolerated, such as in x-ray telescope mirror metrology, it is desirable to measure the mirror as it is mounted in a vertical configuration. By making simple modifications to the standard LTP system, we have demonstrated that it is possible to use the LTP principle to measure the surface of x-ray mirrors and mandrels mounted in the vertical orientation. The major change in the LTP system is the use of a penta prism on a vertical translation stage to direct the probe beam onto the surface and the addition of a precision rotation stage to hold the test object. A 3D map of the surface topography of the complete cylindrical asphere can be generated quite easily with this technique. Measurements with a prototype system indicate a slope error accuracy of better than 1 microradian is possible, with a figure error repeatability of better than 50 nm.