Patent ID: 7508559
Filing Date: 2009-03-24
Classification: G03H

Abstract:
1. A hologram with a surface relief structure that defines at least two patterns capable of reconstruction in a far field, each pattern being sensitive for reconstruction only to radiation of a unique wavelength different from the sensitive wavelength of any other pattern in the surface relief structure, wherein one pattern is sensitive only to radiation that is visible to the unaided eye and another pattern is sensitive only to radiation that is invisible to the unaided eye, wherein the hologram is a single diffractive surface relief element that can reconstruct at least two distinct intensity patterns in the far field on illumination with the said visible and invisible radiation, and the pattern that is sensitive to visible radiation being defined by surface relief features that have a step size that is a function of a first wavelength and the pattern that is sensitive to invisible radiation is defined by surface relief features that have a step size that is a function of a second wavelength.