Terahertz radiation breakthrough smashes efficiency record

Terahertz radiation is extremely useful but, traditionally, tricky and expensive to generate. But scientists at TU Wien have come up with a new source of terahertz radiation that they claim breaks records for efficiency and the breadth of its spectrum, generating a range of wavelengths across the terahertz band.

Like X-Rays, terahertz radiation, or T-Rays, can easily pass through materials. But unlike X-Rays, terahertz radiation is safe. Nestled between radio waves and infra-red light in the electromagnetic spectrum, it isn’t ionizing, and its modest photon energy doesn’t harm living tissue or DNA.

The team’s breakthrough came by focusing efforts at the infra-red end of the range. By passing infra-red laser emissions through a so-called “non-linear medium” the frequency of the radiation is doubled. (For the non-linear media fans out there, those in question were crystals composed of gallium selenide and zinc telluride.)

This higher frequency wave is then added to a conventional infrared laser, creating a new wave with a very particular asymmetric electric field which, according to a TU Wien press release, “is intense enough to rip electrons out of the molecules of the air,” creating a glowing plasma. The field excites electrons in the air, producing the wide band of terahertz radiation in short, sharp pulses.

Though only 2.3 percent of the energy needed is converted into useful terahertz radiation, the researchers say this is orders of magnitude better than other sources. Energy levels approaching 200 µJ (microjoules) were achieved.

TU Wien is relatively vague when it comes to possible applications for this specific technology. “Initial experiments with zinc telluride crystals already show that terahertz radiation is excellently suited to answer important questions from material science in a completely new way,” TU Wien’s Andrius Baltuska says in the press release. “We are convinced that this method has a great future.”

The team’s research paper speculates that the work could lead to relatively affordable terahertz radiation applications built on more readily-available “table-top” laser systems.

Assuming the efficiency breakthrough spells potentially cheaper terahertz radiation, it could one day mean a broadening of its current uses, notably in the security and medical worlds. Not without controversy, it is used for security checks at some airports as it allows security staff to identify items being carried underneath passengers’ clothes. Wood, paper and plastic are also transparent so far as T-Rays are concerned.

Medically, terahertz radiation has seen success in the early detection of various types of cancer, including breast cancer, colon cancer and skin cancer. It’s also been used in dentistry imaging. New Atlas looked at its potential for medical use as far back as 2014.

More experimental uses of terahertz radiation we’ve seen over the years include reading closed books, creating portable particle accelerators, and preventing cars from rusting.

The team’s research has been published in the journal Nature Communications and is available to read online.

Sources: TU Wien, Nature Communications