Researchers from Northwestern University used a light-powered 3D printer to create a terahertz lens. The imaging component is made from a novel metamaterial that exhibits properties not readily available in nature.

The focal length of a lens is determined by its curvature and refractive index, which shapes the light as it enters. Without components to counter imperfections, resulting images can be fuzzy or blurred.

The new lens created by Cheng Sun, associate professor of mechanical engineering, employs a gradient index. The refractive index change changes over space to create flawless images, without requiring additional corrective components.

“Such properties originate from its tiny structures that are much smaller than the terahertz wavelength,” said Fan Zhou, a member of Sun’s laboratory. “By assembling these tiny structures, we can create specific refractive index distribution.”

The lens was manufactured with a 3D printing technique called projection micro-stereo-lithography. The technique enables a scalable, rapid, and inexpensive way to produce the tiny features required for the lens to operate at the terahertz frequency band. The printing technology allowed the researchers to shape the metamaterial to precisely fit their designs.

For fabrication, the researchers used a photo-polymer in liquid form. Light converted the liquid into a solid and the material formed to the shape of the light.

Terahertz imaging provides valuable information for security applications, including the detection of plastic explosives, chemicals, concealed weapons, anthrax, and plastic explosives.

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