Novel 3D printed lens can detect terahertz frequencies

Scientists have 3D printed a novel lens for terahertz frequencies which may lead to high resolution scanners that can detect biological weapons such as anthrax and plastic explosives.
The lens could make terahertz imaging, which is useful for security, cheaper, higher resolution, and more available.
While X-rays can detect metal, they cannot detect plastic or chemicals. Terahertz scanners, however, can detect both of items to discover concealed weapons, biological weapons such as anthrax, and plastic explosives.
Unlike X-rays, terahertz radiation is completely harmless to humans, researchers said.
"This advance means we can unveil previously inaccessible information of some opaque materials in high resolution," said Wei Cao, from the Oklahoma State University in US.

"This opens up an entirely new technique for a massive range of potential uses from biomedical research to security," he said.

The new lens has better imaging capabilities than common lenses, and opens the door for more advances in the mysterious realm of the terahertz, researchers said.
"Typical lenses - even fancy ones - have many, many components to counter their intrinsic imperfections," said Cheng Sun, associate professor at the Northwestern University.
"Sometimes modern imaging systems stack several lenses to deliver optimal imaging performance, but this is very expensive and complex," Sun said.
The new lens employs a gradient index, which is a refractive index that changes over space to create flawless images without requiring additional corrective components.

The lens is made from a novel metamaterial that exhibits properties not readily available in nature.
"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," Zhou said.
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 that are needed for the lens to operate at the terahertz frequency band.
The printing technology allowed the researchers to fabricate the metamaterial to precisely fit their designs.

"For printing, we use a photo-polymer in liquid form. When we shine a light on the material, it converts it into a solid," Sun said.
"The material forms to the shape of the light, allowing us to create a 3D structure. You cannot accomplish a gradient index with traditional manufacturing processes," he said.
The research was published in the journal Advanced Optical Materials.