A proposed method for grating groove density measurement with linear stage by diffraction method

Varied line spacing (VLS) grating can correct the optical aberrations by optimization of the groove density parameters. This kind of grating is widely used nowadays and is the key optical element of high resolution monochromators and spectrometers in VUV and soft X-ray region. The groove density parameters can directly influence the imaging properties of grating and should be measured correctly for performance evaluation of grating spectral instruments. In this paper, a method based on diffraction principal of grating was presented. Different from the conventional diffraction methods which suffer from eccentricity effect and need a high precision rotation stage to get high measuring accuracy, a linear stage instead which is much cheaper was used in this new method. The grating groove density was obtained by measuring the distance of different diffraction orders in one line in this presented method and it is applicable to gratings of arbitrary surface profile. The measuring procedure and the deduced useful formulas would be presented in detail, and the measuring accuracy would be analyzed.