Infrared Imaging Is Coming to Contact Lenses Near You
It’s always good to remind yourself that we as humans only see a very little bit of light. Our slice of the electromagnetic spectrum, the slice known as visible light—sandwiched between the much larger wavelength domains of UV and infrared light—is only about a millionth of the whole range of possible wavelengths that photons exist in. That’s a fun thing to note: we see according to what’s useful for us to see, or what makes sense for us to see given the limitations of biology. But what if we, as would-be post-biological organisms, want to see more of everything, like radio waves or thermal energy hiding in the infrared spectrum? Well, according to research published (but not yet online) today in the journal Nature Nanotechnology, we can have that ability in a contact lens. All it takes is a bit of super-thin wondermaterial graphene and some cleverness.
Basically, when we detect infrared light using a material, we’re looking for electrons freed from that material by the energy delivered by photons from the Sun (or elsewhere). That movement of particles allows us to reconstruct an infrared environment, giving up the locations of heat-bearing animals in the dark or allowing doctors to monitor blood flow. Current IR detectors aren’t so tiny as to be wearable yet, but the paper argues graphene, essentially single atom-thick chickenwire, is the answer, providing a material small and thin enough to be incorporated into a contact lens.
The catch with graphene, which has long been studied for its photonic potential, is that it only captures about 2.3 percent of whatever light energy it’s bombarded with. This makes it inefficient as a light detector. But, what the new research demonstrates is that it’s possible to sandwich graphene with a very thin sheet of some other material carrying an electrical current. While the inbound light might not shake enough electrons loose from a graphene sheet to be useful alone, with this second current-bearing material, it’s possible to register the spaces left by exiting electrons in the graphene as a change in the electrical field of the second material. The result is still thin and tiny enough to fit on a pinky fingernail.
(1) Graphene is a two-dimensional crystal consisting of a single layer of carbon atoms arranged hexagonally; (2) The band structure of a representative three-dimensional solid (left) is parabolic, with a band gap between the lower-energy valence band and the higher-energy conduction band. The energy bands of two-dimensional graphene (right) are smooth-sided cones, which meet at the Dirac point; (3) A flake of exfoliated graphene 50 micrometers square was placed on layers of silicon dioxide insulator and a silicon gate. The schematic, left, shows how gold contacts were attached to the graphene to apply gate voltage. A 10-micrometer beam of infrared synchrotron radiation (red spot) was focused onto the graphene to measure transmission and reflectance spectra; (4) The conductivity of graphene at different gate voltages, graphed here by curves of different colors, was observed to change with frequency. At high energies (high frequencies), right, conductivity and thus absorption was the same for all voltages, but at energies below a threshold at twice the Fermi energy, the absorption of infrared light decreased. Inset shows the Fermi energy (horizontal lines) and the absorption threshold at twice the Fermi energy (vertical arrows) on a graphene band-structure diagram [source]
"Our work pioneered a new way to detect light," says Zhaohui Zhong, an assistant professor of electrical engineering and computer science at the University of Michigan. "We envision that people will be able to adopt this same mechanism in other material and device platforms."
While military and scientific applications are ready-made, for the rest of us it’s a question of whether we even want to have an entirely new layer of visual experience/stimulus on top of regular old, complex visible light. "If we integrate it with a contact lens or other wearable electronics, it expands your vision," Zhong says. "It provides you another way of interacting with your environment." Which begs the question, Can we even handle another way of interacting with our environment? Or should we just leave infrared to snakes and trippy photographers?