The concept of using a perforated metal film and plasmons to selectively filter light at specific frequencies is not entirely new, but scientists have assumed that the only way to achieve the transmission of radiation through a film has been to use a uniform, or periodic, array of holes. However, what the Utah researchers showed, in the current issue of Nature, was that the perforations did not need to be uniform at all. In fact, in spite of the seemingly haphazard array of holes, nearly all of the terahertz energy was transmitted through the metal. However, the main benefits of discovering that any array of holes can transmit so much energy, says Nahata, is that it gives more freedom to design filters for various frequencies. “We’re not just limited to periodic structures,” he says.
The research could be a boon to terahertz device engineering, which is still in its infancy, says Daniel Mittleman, professor of electrical engineering at Rice University. “There aren’t many devices for manipulating terahertz radiation,” he says. “Any additional knobs that we have to control the terahertz wave are good.” The Utah work is a step toward shaping and selecting terahertz waves, he says.
Discovering that a non-periodic array of holes in a film can transmit terahertz energy is “really something new,” says Martin Koch, professor of electrical engineering and information technology at the Braunschweig Technical University, in Germany. Koch is the director of Braunschweig’s Terahertz Communication Lab, which opened last year, with the goal of building terahertz devices for the next generation of wireless communication. He suspects that terahertz devices are still at least a decade away from being made, and he says that it is currently unclear whether or not the Utah research will be directly applicable to them. However, Koch adds that the work is “nice, fundamental research that I’ll keep in the back of my mind.”
Nahata agrees that terahertz communication devices are many years away, but in the meantime, the work could also help researchers better understand terahertz physics and apply it to applications such as safer replacement for x-rays. (See “Taming the Terahertz.”)