Two-dimensional groove density measurement for gratings by diffraction method

A grating groove density measuring system based on diffraction method has been developed to measure the two-dimensional groove density variations of the VLS gratings at NSRL. The measuring system can provide not only the basic data of the two-dimensional groove density variations for evaluating the imaging properties of grating, but also an important tool for improving the grating manufacturing technology. A commercially available concave grating with a curvature radius of 750 mm was measured to test the accuracy of the measuring system. Results show that the system has a measuring accuracy (ΔN/N) of about 5 × 10⁻⁵. Then the groove density variation parameters of the 1200 lines/mm VLS plane grating used in NSRL is measured by the system. The groove curvature of the VLS plane grating has been observed.