New research could lead to the birth of a generation of light detectors that can see below the surface of bodies, walls, and other objects.
Using graphene (made from a one-atom-thick layer of carbon) a prototype detector was able to see a broad band of wavelengths. Some of these wavelengths, such as terahertz waves, are invisible to the human eye and difficult to detect, the University of Maryland reported.
"[The detector] could find applications in emerging terahertz fields such as mobile communications, medical imaging, chemical sensing, night vision and security," said lead author Xinghan Cai, a UMD physics graduate student.
Terahertz light waves' long wavelengths and low frequencies put them somewhere on the scale between microwaves and infrared waves. The light can was through opaque materials such as skin, cardboard, and plastic. It can be used to identify chemical signals emitted exclusively in the terahertz range.
There are currently very few methods for detecting terahertz light. In order to maintain sensitivity most detectors must be kept at extremely low temperatures such as negative 452 degrees Fahrenheit; these detectors also tend to be bulky and slow.
This new temperature detector solves these problems using graphene, which has the ability to increase the speed and maintain the sensitivity of the terahertz wave detector at room temperature. A new operating principle called the "hot-electron photothermoelectric effect" allowed the team to create the improved device. Graphene works in light detection because when light is absorbed by electrons suspended in the honeycomb lattice of the graphene they retain the energy.
"[In the method] Light is absorbed by the electrons in graphene, which heat up but don't lose their energy easily. So they remain hot while the carbon atomic lattice remains cold," said UMD Physics Professor Dennis Drew.
The electrical signal detects the presence of the terahertz waves beneath the surface of the opaque material. X-rays look straight through skin into the bone, but miss the layers right below the surface, terahertz waves allow researchers to see the in-between layers.
The findings were published Sept. 7, 2014 in the journal Nature Nanotechnology.
