Ultra-thin Detector Captures Unprecedented Range of Light

New research at the University of Maryland could lead to a generation of light detectors that can see below the surface of bodies, walls, and other objects.

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.

A research paper about the new detector was published online Sept. 7, 2014 in the journal Nature Nanotechnology. Lead author Xinghan Cai, a UMD physics graduate student, said a detector like the researchers’ prototype “could find applications in emerging terahertz fields such as mobile communications, medical imaging, chemical sensing, night vision and security.”

The light we see illuminating everyday objects is actually only a very narrow band of wavelengths and frequencies. 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. 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 realized, 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, around 4 Kelvin, or -452 degrees Fahrenheit. 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 U.S. Naval Research Lab and Monash University, Australia, gets around these problems by using graphene, a single layer of interconnected carbon atoms. By utilizing the special properties of graphene, the research team has 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,” says Michael Fuhrer, professor of physics at UMD and Monash University.

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