Importance

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Abstract

A security device, including at least first and second embossed, reflective metal diffraction gratings in respective regions: wherein the first diffraction grating exhibits, in incident white light, a zero-order output over a first area of substantially uniform grating period, wherein the zero-order output of the first diffraction grating comprises different coloured first and second sub-outputs for respective first and second polarisations parallel and perpendicular to the first diffraction grating; wherein the second diffraction grating exhibits, in incident white light, a zero-order output over a second area of substantially uniform grating period; wherein the zero-order output of the second diffraction grating comprises third and fourth sub-outputs for respective first and second polarisations parallel and perpendicular to the second diffraction grating; and wherein the first and second diffraction gratings exhibit, for incident white light, substantially the same first order diffraction efficiency over the first and second areas.

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First Claim