T-rays: What a Bright Future

Scientists Beef up Faint Energy

By A.J. Hostetler, Times-Dispatch
November 14, 2002

Using the powerful laser at the Jefferson Lab, scientists can muster a souped-up beam of radiation 100,000 times brighter than with previous sources.

Terahertz radiation, known as T-rays, was emitted when electrons whizzing along at nearly the speed of light were deflected by a magnetic field. The seemingly faint energy - that of five nightlights - demonstrates T-rays' potential for medical imaging, communications and even quality control.

T-rays are emitted by all the objects around you, but they cannot be seen by humans. T-rays can go through just about anything except metal and water. People who spend serious time thinking about T-rays say this ability, the result of their short wavelengths, make them ideal candidates for certain types of medical imaging.

Among other potential uses imagined are: safer versions of X-rays; scanning baggage at airports; identifying large biological molecules such as proteins, viruses and bacteria; and even measuring the effectiveness of facial moisturizers.

T-rays are part of the broad spectrum of electromagnetic radiation that includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.

They cycle at a trillion ("tera") cycles per second, compared to the fastest PC that runs at a mere 2.4 gigahertz, which cycles in billions per second.

Scientists say that by using T-rays in the same way that radio waves are used to carry signals to and from cell phones, they could create new methods of wireless communication.

Alas, although scientists were talking about how they wanted to use T-rays, no one knew how to make them bright enough to actually use in the everyday world.

It was like designing a car before figuring out how to build the engine. Attempts with semiconductors produced only wimpy T-rays, 1/2,000th of a watt at most.

Now, photon scientist Gwyn Williams and colleagues have used the free-electron laser at the Thomas Jefferson National Accelerator Facility in Newport News to produce T-rays with the power of 20 watts. A typical nightlight produces 4 watts.

"Think of a candle and then think of a floodlight," said Williams, who describes the experiment in today's Nature. He hopes to soon coax a couple hundred watts of T-rays out of the laser.

The Jefferson Lab's "spectacular result" came when scientists shifted from running electrons through semiconductors to sending them through the vacuum inside a particle accelerator, said Mark Sherwin, a physicist at the University of California in Santa Barbara.

"I was surprised when I heard the words '20 watts' and 'terahertz' in the same sentence," said Sherwin, who wrote about the radiation's potential applications for the journal Nature.

Williams and his colleagues used the Jefferson Lab's free-electron laser setup as a racetrack for electrons. The laser shot millions of electrons down a 60-foot-long column at nearly the speed of light. They hurtled down the straightaway bunched in a pack until - wham - they plowed through a magnetic field.

The smack upside the head diverted the electrons' path, loosening some of their energy, which they released as light. There was so much that the physicists were able to recycle almost all the energy.

That efficiency will be important as scientists try to move the experiment from the underground world of the Jefferson laser to a tabletop version with industrial or commercial applications.

Ever since word about the Jefferson Lab's experiment got out last December, physicists have been fantasizing about what one called "killer applications" for T-rays.

Thoughts of using T-rays to help airline pilots peer through fog or help manufacturers check the number of raisins in cereal have been on hold because of the inability to make sufficiently powerful - and relatively cheap - rays.

Publication of the Jefferson Lab's feat should now spur interest in the underutilized T-rays from some very different fields.

"The growing awareness of T-rays' usefulness is like what happened a century ago with X-rays - only T-rays will have a much wider range of applications," Williams said.