Measurement of period difference in grating pair based on analysis of far-field intensity patterns

We propose and demonstrate an experimental method for measuring the period difference in grating pair. The method uses the compensating relationship between line-density difference and the Littrow-angle difference of gratings. Far-field intensity patterns of 0th- and −1st-orders diffraction beams are monitored for alignment during the angle measurement. For a pair of ∼0.676 μm period gratings, the relative period difference was measured to be 798.4 × 10−6 with a standard deviation of 2.0 × 10−6.