Miniaturization of optical structures makes it possible to control light at the nanoscale, but on the other hand it imposes a challenge of accurately handling numerous unit elements in a miniaturized device with aperiodic and random arrangements. Here, we report both the new analytical model and experimental demonstration of the photon sieves with ultrahigh-capacity of subwavelength holes (over 34 thousands) arranged in two different structural orders of randomness and aperiodicity. The random photon sieve produces a uniform optical hologram with high diffraction efficiency and free from twin images that are usually seen in conventional holography, while the aperiodic photon sieve manifests sub-diffraction-limit focusing in air. A hybrid approach is developed to make the design of random and aperiodic photon sieve viable for high-accuracy control of the amplitude, phase and polarization of visible light. The polarization independence of the photon sieve will also greatly benefit its applications in optical imaging and spectroscopy.
The new "ultra-capacity nano-photon sieve" can incorporate more than 34,000 nanoholes randomly distributed in its surface. (Credit: Bastian Eichhorn/Flickr)
Scientists have found a way to potentially prevent counterfeit in currency, documents, credit cards, and even IDs.
Many modern documents include holograms to enhance the security, and they are generally difficult to replicate outside of an optical lab.
Although accurate recreation of these holograms is extremely challenging, a similar shiny, multi-colored look can be created using a mixture of pigments and base, and this may pass a quick inspection.
The new technology aims at higher-level security measures rather than street-level counterfeiting.
The team designed an “ultra-capacity nano-photon sieve”—a unique device with the capacity to incorporate more than 34,000 nanoholes (~300nm in diameter) randomly distributed in its surface.
This feature enables the display of a high-pixel and high-quality holographic image at a controlled position.
“Highly secured virtual information is stored in the collection of these nanoholes and they can only be retrieved and read at a particular distance when a proper polarized illumination is employed,” explains Qiu Cheng-Wei, assistant professor at the National University of Singapore.
“Our device can be customized for various applications as the dimensionality (for example, two-dimensional or three-dimensional), display distance, polarization, and wavelength dependence can be tailored according to needs.”
The team’s new technology could open up a new optic avenue for unparalleled security at nanoscale precision.
“We are looking into making our system more robust, developing multiple holographic images at multiple displaying planes, wavelength-dependent, or polarization-dependent three-dimensional images, higher pixels, and other emerging applications enabled by the capability of handling such a huge quantity of nanoholes,” says Qiu.
The findings appear in Nature Communications.
Source: National University of Singapore
http://www.futurity.org/counterfeit-nano-holes-953742/
http://www.nature.com/ncomms/2015/150505/ncomms8059/full/ncomms8059.html
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