Two-Dimensional Measurement of Groove Spacing for Plane VLS Gratings Using the Long Trace Profiler

We proposed a diffractive method of absolute measurement of groove spacing for plane varied-line-spacing (VLS) gratings based on the long trace profiler. It was demonstrated over sub-nanometer measurement accuracy in determining the groove spacing of a grating with grooves varying in sub-micrometer scale along its surface. Being sensitive to angle measurement (sub-murad), the long trace profiler (LTP) was used to measure the groove density (or the groove density variation) of a surface diffraction grating along its longitudinal direction. Based on Littrow mounting configuration, the accuracy of groove density measurement exceeded 1 times 10^-4 on the whole surface. Equipped with one linear guide, it easily afforded two-dimensional measurement of groove density for a diffraction grating quickly