by Txchnologist staff

A new energy detector that can pick up terahertz radiation could open the door to a new era of imaging in fields from medicine to security screening and food inspection.

Researchers around the world have been working for decades to create a material that efficiently detects the terahertz portion of the electromagnetic spectrum. These wavelengths of energy, which are longer than visible light and sit between infrared and microwave on the spectrum, have characteristics that make them useful for a number of applications.

They can penetrate through fabrics and certain materials like plastic, making them useful in screening for weapons or contraband. They can also move through a few millimeters of tissue without damaging DNA or injuring cells before bouncing back, enticing medical imaging researchers who think the energy could be used to detect certain cancers and cavities in teeth without the need for X-rays or large MRI machines.

“The potential improvements in size, ease, cost and mobility of a terahertz-based detector are phenomenal,” said Rice University physicist Junichiro Kono, who has been working on a terahertz detector. “With this technology, you could conceivably design a handheld terahertz detection camera that images tumors in real time with pinpoint accuracy. And it could be done without the intimidating nature of MRI technology.”

But a major obstacle has been finding a material that could absorb terahertz and turn it into electrical signals for processing.

“The photonic energy in the terahertz range is much smaller than for visible light, and we simply don’t have a lot of materials to absorb that light efficiently and convert it into an electronic signal,” said Sandia National Laboratories physicist François Léonard, who worked with Kono on a solution. “So we need to look for other approaches.”

Now scientists from several institutions including Kono and Léonard have published a paper in the journal ACS Nano Letters that says they’ve built an efficient and flexible detector that operates at room temperature and without needing an external source of power.

To do it, they have used microscopic rolls of linked carbon atoms called carbon nanotubes to make a compact device. They say it works through the full terahertz spectrum of wavelengths and could lead to advances in medicine, communications, security applications, bioengineering, astronomy and environmental monitoring.

Sandia’s Léonard said carbon nanotubes are extremely good at absorbing terahertz electromagnetic energy. And because nanotubes have properties that make them both electric conductors and semiconductors at the same time, making a film out of them created an exceptional detector surface.

“The structure is very compact and combines the absorber, the thermometer and polarizer that terahertz detectors require into one piece of film,” said Rice graduate student and lead author Xiaowei He.

In the next phase of their work, the researchers will improve their system’s efficiency and connect a terahertz radiation generator to serve as a source.

“We have some very clear ideas about how we can achieve these technical goals,” said Léonard. “Our technical accomplishments open up a new path for terahertz technology.”

Top Image: Researchers at Sandia National Laboratories, Rice University and the Tokyo Institute of Technology developed a terahertz detector using several nanoscopic-sized tubes, creating a macroscopic thin film that contains a mix of metallic and semiconducting carbon nanotubes. Photo courtesy Dino Vournas/Sandia National Laboratories.