Soon, detector to see objects invisible to naked eye

Scientists are working on a gen-next ultra-thin detector that can see below the surface of bodies, beyond walls and other objects invisible to the human eye.
Using the special properties of graphene, a two-dimensional form of carbon that is only one atom thick, a prototype detector is able to see an extraordinarily broad band of wavelengths.
Included in this range is a band of light wavelengths that have exciting potential applications but are notoriously difficult to detect: terahertz waves, which are invisible to the human eye.
Lead author Xinghan Cai, a University of Maryland (UMD) physics graduate student, said a detector like the prototype "could find applications in emerging terahertz fields such as mobile communications, medical imaging, chemical sensing, night vision and security."

Terahertz light waves' long wavelengths and low frequencies fall between microwaves and infrared waves.
The light in these terahertz wavelengths can pass through materials that we normally think of as opaque, such as skin, plastics, clothing and cardboard, researchers said.

It can also be used to identify chemical signatures that are emitted only in the terahertz range.
Few technological applications for terahertz detection are currently realised, however, in part because it is difficult to detect light waves in this range.
In order to maintain sensitivity, most detectors need to be kept extremely cold. Existing detectors that work at room temperature are bulky, slow and prohibitively expensive.

The new room temperature detector, developed by the UMD team and colleagues at the US Naval Research Lab and Monash University, Australia, gets around these problems by using graphene, a single layer of interconnected carbon atoms.
By utilising the special properties of graphene, researchers have been able to increase the speed and maintain the sensitivity of room temperature wave detection in the terahertz range.
Using a new operating principle called the "hot-electron photothermoelectric effect," the research team created a device that is "as sensitive as any existing room temperature detector in the terahertz range and more than a million times faster," said Michael Fuhrer, professor of physics at UMD and Monash University.

Graphene, a sheet of pure carbon only one atom thick, is uniquely suited to use in a terahertz detector because when light is absorbed by the electrons suspended in the honeycomb lattice of the graphene, they do not lose their heat to the lattice but instead retain that energy.
The research was published in the journal Nature Nanotechnology.