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 moiré 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 moiré patterns. Two particular applications are treated: increased sensitivity from fringe multiplication in a moiré display and examination of the element-profile shape of gratings. Moiré procedures with two, and with multiple, gratings are discussed. Indications of moiré pattern microstructures and moiré fringe profiles are indicated.