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Terahertz Radiation or T-Rays

Sending tight bunches of electrons at nearly the speed of light through a magnetic field causes the electrons to radiate T-rays at a trillion cycles per second—the terahertz frequency that gives T-rays their name and that makes them especially useful for investigating biological molecules.

Invisible T-rays bear comparison with radio waves, microwaves, infrared light and X-rays. But unlike those much-used forms of radiated energy, up until recently T-rays have been little exploited—in part because no one knew how to make them bright enough.

T-rays are electromagnetic radiation of the safe, non-ionizing kind. They can pass through clothing, paper, cardboard, wood, masonry, plastic and ceramics. They can penetrate fog and clouds. Their wavelength—shorter than microwaves, longer than infrared—corresponds revealingly with biomolecular vibrations.

For over a decade, scientists worldwide have been pressing the study of terahertz light and looking for better ways to generate and use it. An Aug. 16, 2002, Science magazine article, "Revealing the Invisible," reported that "much research is being directed toward the development of T-ray sources and detectors, particularly for applications in medical imaging and security scanning systems." The Web site of Dr. Xi-Cheng Zhang, a T-ray expert at Rensselaer Polytechnic Institute, predicts that "the future 'killer application' ... will be in biomedicine."

Overall, though, T-rays still constitute a gap in the science of light and energy. They inhabit a region of the electromagnetic spectrum remaining to be better understood—and much better exploited. Now that a way to generate them at high power has been demonstrated, T-rays can potentially extend and add widely to the wave-based technologies that have defined the last century and a half, from the telegraph, radio and X-rays to computers, cell phones and medical MRIs.

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T-rays in the Electromagnetic Spectrum. (Courtesy: Jefferson Lab)

Various lightsources around the world can produce Terahertz light and are beginning to develop research programs for Terahertz light.

But no matter how bright they are, T-rays can't penetrate metal or water. So they can't be used to inspect cargo containers on arriving ships or to diagnose conditions deep inside the human body. However, 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. Scientists’ task is to develop those uses individually.

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T-rays in the Electromagnetic Spectrum. (Courtesy: Jefferson Lab)
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