| 摘要 |
An iridescent material comprises a diffraction grating incorporating a plurality of sheets (1) of a first substantially transparent material in parallel alignment and spaced away apart by quantities of a second substantially transparent material (2), the second material having a refractive index significantly lower than the refractive index of the first material, the plates being tilted at an angle &thetas; to an axis X and the grating having a period d(X) in the direction of axis X, the angle &thetas; and period d being such that a second diffraction grating is provided along an axis Z, perpendicular to axis X, the second diffraction grating having a period d(Z) and consisting of ten periods or less and whereby, the diffraction conditions of the grating can be simultaneously fulfilled by electromagentic radiation of a range of wavelength thereby causing iridescence. Materials according to the invention have applications in inter alia document security, anti-counterfeiting measures, artwork, gift wrapping paper and cards and clothing design. |
