Abstract
A long trace profiler method has been developed to measure the groove density of concave gratings in National Synchrotron Radiation Laboratory recently. With the aid of large angular acceptance (35mrad), it is suitable for precise measurement of concave or convex gratings with high curvatures. The effects of the slope variations along its substrate are discussed in detail. To eliminate the off-axis errors, which are the essential error sources in the measuring system based on rotating mounts of gratings, an error-reduced method is introduced consequently. A commercially available concave grating with a curvature radius of 998mm is measured and the relative groove density error δN∕N is about 4×10−5 rms.
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