Moiré and higher grating harmonics

The conditions for and formation of low-spatial-frequency beat patterns between superposed grid structures are studied. The application of moire techniques for Fourier analysis of incoherently illuminated distributions is demonstrated. The different multiples of the fundamental spatial frequency of a grating are used to form distinguishable moire patterns. Two particular applications are treated: increased sensitivity from fringe multiplication in a moire display and examination of the element-profile shape of gratings. Moire procedures with two, and with multiple, gratings are discussed. Indications of moire pattern microstructures and moire fringe profiles are indicated.