An imaging grating diffractometer for traceable calibration of grating pitch in the range 20 μm to 350 nm

This work describes the development of a grating diffratometer to provide traceable calibration of grating pitch in range 20 mu m to 350 nm. The approach is based on the Littrow configuration in which a laser beam is directed onto the grating which is mounted on a rotary table and can be turned so that each selected diffraction order is retro-reflected in the laser incidence direction. A beamsplitter and a lens direct the reflected diffraction order to form a small image spot on a CCD camera and the spot centering is used to adjust to rotation angle, thereby giving the diffraction angle. Knowing the diffraction angle for several orders and the wavelength of the laser, the average grating pitch can be determined to an uncertainty the order of 14 pm.