Metamaterials, with the ability of tailoring optical properties of materials, have been applied to holograms recently, which has shown the priorities of switchable polarization and multicolor image comparing with the conventional holograms. However, the current metasurface based multicolor holograms have suffered the problems of narrow band and low efficiency in phase modulation for gold and silver when their feature dimensions are in few tens of nanometers. Interestingly, aluminum with higher plasma frequency could yield surface plasmon resonance across a broader range of the spectrum ranging from visible to UV. Metasurfaces incorporating with the aluminum offer the unique opportunity to extend the working wavelength to cover the entire visible spectrum for the generation of full color meta-holograms.
Here we demonstrated a phase modulated multicolor meta-hologram that is polarization dependent and capable of producing images in red, green and blue colors. The metahologram is made of aluminum nanorods that are arranged in a two-dimensional array of pixels with surface plasmon resonance in the visible to UV range. The aluminum nanorod array is patterned on a 30 nm thick SIO2 spacer layer sputtered on top of a 130nm thick aluminum mirror. With proper design of the structure, we obtain resonances of narrow bandwidths to allow for implementation of multicolor scheme. Taking into account of the wavelength dependence of the diffraction angle, we can project images to specific locations with predetermined size and order. With tuning of aluminum nanorod size, we demonstrate that the image color can be continuously varied across the visible spectrum.
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