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JUL/AUG 2013  

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'Flat Lens' Creates 3-D Images in Free Space

Scientists working at the National Institute of Standards and Technology (NIST) have demonstrated for the first time a new type of lens that bends and focuses ultraviolet (UV) light in such an unusual way that it can create ghostly, 3-D images of objects that float in free space, according to NIST.

The easy-to-build lens could lead to improved photolithography, nanoscale manipulation and manufacturing, and even high-resolution three-dimensional imaging, as well as a number of as-yet-unimagined applications in a diverse range of fields.

“Conventional lenses only capture two dimensions of a three-dimensional object,” says NIST's Ting Xu. “Our flat lens is able to project three-dimensional images of three-dimensional objects that correspond one-to-one with the imaged object.”

Nist lens

A NIST team has created an ultraviolet metamaterial formed of alternating nanolayers of silver and titanium dioxide. The metamaterial has an angle-independent negative refractive index, enabling it to act as a flat lens. When illuminated with UV light (purple) a sample object of any shape placed on the flat slab of metamaterial is projected as a three-dimensional image in free space on the other side of the slab. Here a ring-shaped opening in an opaque sheet on the left of the slab is replicated in light on the right. Credit: Lezec/NIST

The new lens is formed from a flat slab of metamaterial with special characteristics that cause light to flow backward—a counterintuitive situation in which waves and energy travel in opposite directions, creating a negative refractive index, according to NIST.

A negative-index flat lens like this also has been predicted to enable the transfer of image details substantially smaller than the wavelength of light and create higher-resolution images than are possible with lenses made of positive-index materials such as glass.

The lens has a focal length of about half a millionth of a meter—challenging to achieve with conventional refractive optics such as glass lenses—and the metamaterial can be turned on and off using higher frequency light as a switch, allowing the flat lens to also act as a shutter with no moving parts.

The lens will offer other researchers greater flexibility for manipulating UV light at small length scales, according to NIST. With its high photon energies, UV light has a myriad of applications, including photochemistry, fluorescence microscopy and semiconductor manufacturing. That, and the fact that the lens is so easy to make, should encourage other researchers to explore its possibilities, NIST reports.

The new work was performed in collaboration with researchers from the Maryland NanoCenter at the University of Maryland, College Park; Syracuse University; and the University of British Columbia, Kelowna, Canada.

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