Measurements of the diffraction characteristics of one-dimensional surface-relief gratings of locally varying profile are compared with rigorous diffraction theory. These gratings result from the superposition of two linear sinusoidal gratings of uniform depth for which the relative phase between the two gratings varies slowly with position. The resultant surface profile exhibits a relatively large-period variation in profile form. The periodic variation in diffraction efficiency that results yields a visual moiré pattern that has interesting asymmetry and polarization properties that alter as the viewing conditions are changed; the gratings can be exploited by diffractive optically variable devices for document security.
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