Moiré Screens Coded with Pseudo-Random Sequences

A new type of moiré grating that can produce very narrow moiré beat lines is presented. Each grating period contains a number of transparent or opaque lines of equal width. The sequence of transmission coefficients across the grating period is not periodic but is chosen to be a binary pseudo-random sequence. These sequences are commonly used in signal processing because of their sharply peaked autocorrelations. When used to encode a moiré grating, they produce very narrow moiré beat lines. Three experimental gratings are discussed, and a contouring measurement using the narrow beat lines is described.