Groove Density Measurements for the VLS grating by Diffraction Method

A grating groove density measurement system is developed to measure the groove variation of VLS grating in NSRL. It has certain advantages over methods like Atomic force microscopy(AFM), Moiré fringe method and long trace profiler(LTP). It is applicable to gratings of arbitrary surface shape and with arbitrary groove density distribution. The errors affecting the measurement accuracy are analyzed. The mechanical setup sketch is given. The mechanical accuracy is calibrated in order to control the uncertainty. The first result of a VLS plane grating is tested. The system accuracy (ΔN/N) is about 2×10−4.