Color selectivity of surface-plasmon holograms illuminated with white light
Spotlight summary: Holography, since its conception 67 years ago, remains a fascinating 3D imaging method and by its very nature is a monochromatic imaging tool. This “monotonous” way of recording a hologram has now been given the ability to record and display true color images by a team led by Satoshi Kawata at RIKEN Institute, Osaka, Japan.
Currently all 3D image projection technologies including the 3D movies and 3D television sets produce the images of the objects that are nothing more than pairs of 2D images perceived as 3D objects by the brain based on the effect of lateral parallax. A hologram can display a true 3D image of an object or scene recorded by a coherent light source and reconstructed by illuminating it with a white light producing single color images at selective angles. The new holographic method, called surface plasmon holography, developed by the authors of this article, overcomes the color and visibility limitations of the conventional hologram.
Light induced electron charge density oscillations and associated electromagnetic fields on the surface of a metal are called surface plasmon-polariton (SPP) waves. The new technique is based on the property of surface plasmons that for each color of light, plasmon resonance can happen only at a particular angle between the incident light and the metallic film.
The key to a surface-plasmon hologram is a thin metallic layer coated onto a photoresist (precoated on a glass plate) that makes up the hologram. The hologram is recorded on the photoresist by the interference of a scattered field from the object and a reference light field. Three exposures are made using lasers (red, blue and green) at three different angles. When this SPP hologram is illuminated by white light through a prism in total internal reflection geometry, the evanescent field generated in the metal film gets associated with the surface plasmons and is converted into radiative light field by the grating structure of the hologram. The red, blue and green images are reconstructed (which mix together to display the true 3D color image of the object) by satisfying the resonance conditions of surface plasmons for individual colors.
In the current work, the authors of this article demonstrate the optimization of color selectivity and spatial color uniformity of SPP holograms. The color selectivity can be tuned by controlling the thicknesses of the dielectric layer and the plasmonic metal layer to 25 nm and 55 nm for silicon dioxide and silver, respectively. They propose to use holograms made of silver film corrugations for better color uniformity over the dielectric holograms on flat silver film.
Some limitations of the system remain to be improved on, such as imaging larger objects and increasing the viewing angle for stereo images that are currently limited to about 25 degrees.
Holography is an inherently 3D technology that is now capable of full color image display. Combination of surface plasmons and holography can have potential applications in mobile device displays and 3D vision experience, with images and movies closer to the real world.
Technical Division: Optical Design and Instrumentation
ToC Category: Holography
|OCIS Codes:||(090.2870) Holography : Holographic display|
|(240.6680) Optics at surfaces : Surface plasmons|
|(090.1705) Holography : Color holography|
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