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Published on May 3rd, 2016 | By: Stephanie Liverani


Light-powered 3-D printing technique creates new terahertz lens for better security imaging

Published on May 3rd, 2016 | By: Stephanie Liverani

[Image above] Credit: Matteo Lena; Flickr CC BY-NC 2.0


Thinner, more flexible lenses are paving the way for innovations in imaging technology with seemingly limitless potential applications.


When it comes to developing ultrathin lenses, scientists at the Australian National University (Canberra, Australia) may have changed the game. The team created what it describes as “the world’s thinnest lens, one two-thousandth the thickness of a human hair,” which could revolutionize flexible computer displays and miniature cameras, according to an ANU press release.


More recently, researchers from Columbia University’s School of Engineering and Applied Science (New York City, N.Y.) are developing a new flat, thin camera that is so flexible it can be wrapped around objects to capture images that can’t be taken with conventional cameras—even with multiple camera setups. The team designed and fabricated a flexible lens array that adapts its optical properties when the sheet camera is bent.


And now engineers at Northwestern University’s McCormick School of Engineering (Evanston, Ill.) are working on a new lens that could be used for biomedical research and security imaging: a terahertz lens created by a light-powered 3-D printer.


So why is terahertz the key wavelength of focus in this research?


On the electromagnetic spectrum, “terahertz is somewhat of a gap between microwaves and infrared,” Cheng Sun, associate professor of mechanical engineering at Northwestern, says in a university news release about the work. “People are trying to fill in this gap because this spectrum carries a lot of information.”


Developing this lens required two major factors, the release explains.


First, it’s 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,” Fan Zhou, first author of the research and member of Sun’s laboratory, says in the release. “By assembling these tiny structures, we can create a specific refractive index distribution.”


Second, the team used projection micro-stereo-lithography to create the lens—a technique that enables a fast, inexpensive, and scalable way to produce the tiny features necessary for the lens to effectively operate at the terahertz frequency band, the release explains.


(Check out this quick video that shows Sun’s team printing a stent with the same technology used to print the terahertz lens.)

Credit: Northwestern Engineering; YouTube


“For printing, we use a photo-polymer in liquid form,” Sun says. “When we shine a light on the material, it converts it into a solid. The material forms to the shape of the light, allowing us to create a 3-D structure. You cannot accomplish a gradient index with traditional manufacturing processes.”


The lens could revolutionize security imaging as a cheaper, higher-res, safer alternative to more traditional X-ray imaging.  


While X-rays can detect metal, the release explains, they cannot detect plastic or chemicals. Terahertz scanners can detect metal, but also biological weapons such as anthrax and plastic explosives without the potential harmful side effects that X-ray exposure poses to humans.


“This advance means we can unveil previously inaccessible information of some opaque materials in high resolution,” Wei Cao, Sun’s collaborator at Oklahoma State University, says in the release. “This opens up an entirely new technique for a massive range of potential uses from biomedical research to security.”


The research, published in Advanced Optical Materials, is “Additive manufacturing of a 3-D terahertz gradient-refractive index lens” (DOI: 10.1002/adom.201600033).


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