Diffraction from metallic gratings with locally varying profile forms

Measurements of the diffraction characteristics of one-dimensional surface- relief gratings of locally varying profile are compared with rigorous diffr action theory. These gratings result from the superposition of two linear s inusoidal gratings of uniform depth for which the relative phase between th e two gratings varies slowly with position. The resultant surface profile e xhibits a relatively large-period variation in profile form. The periodic v ariation in diffraction efficiency that results yields a visual moire patte rn that has interesting asymmetry and polarization properties that alter as the viewing conditions are changed; the gratings Lean be exploited by diff ractive optically variable devices for document security. (C) 1999 Optical Society of America.