Measurement of diffraction gratings with a long trace profiler with applications for synchrotron beamline gratings

摘要

The Long Trace Profiler (LTP) is used primarily for measuring the figure of long synchrotron beamline mirrors. The LTP has also been used for measuring the figure of the substrate of beamline gratings. We propose a method for measuring the effective figure that comes from the gratings groove pattern on the substrate of long beamline gratings. Analysis of gratings groove patterns can be useful in determining cause of poor imaging of the diffracted light, but requires investigation of small changes of the groove frequency over the entire clear aperture of the grating. A diffraction grating that is small enough to be measured by a general purpose six inch aperture interferometer is measured by both this interferometer and the LTP, so that results for two different instruments may be compared. The height profile of the substrate light (m = 0) measurement is subtracted from the height profile of the diffracted light (m = 1) measurement, and the result is the effect of only the diffraction from the grooves along the entire surface. This procedure is also used for a diffraction grating that is too long to be measured by the general purpose interferometer, but is easily measured by the LTP.