A team has developed a lens that can image on the terahertz wavelength. Defining terahertz as “somewhat of a gap between microwaves and infrared,” Cheng Sun, from Northwestern University’s McCormick School of Engineering, has described the mysterious range as little understood and rarely studied.

Gradient refractive image lens design. Image credit: Northwestern University But Sun’s team created a lens using a 3D printer that can image in the range, and could be used to advance biomedical research as well as security imaging, among other applications.

To create the lens, they had to overcome the common imperfections that today’s lenses encounter: the curvature and refractive index that shapes entering light must be perfect to create images that are not fuzzy or blurred. It is not uncommon for imaging systems to stack lenses on top of each other to correct imperfections and attain optimal performance, however the process is costly and complicated.

Using metamaterials and a 3D printer, Sun’s lens overcomes these imperfections to create a single lens that puts out a near-perfect image. It then is printed using a gradient index: a refractive index that changes over space, to create flawless images without the need for corrective components. The ability to use a metamaterial made the discovery possible; the novel material has structures smaller than the terahertz wavelength, giving them the ability to develop a specific refractive index distribution by assembling the structures. Additionally, using a photo-polymer in liquid form, projection micro-stereo-lithography 3D printing allowed them to yield the features necessary for the lens to operate, and to fabricate the metamaterial to fit the design precisely.