Washington, Nov. 23 : An international team led by Ulrich Welp at Argonne National Laboratory in Illinois, US, has come closer to producing a beam of terahertz waves or 'T-rays' that could revolutionise airport security and medical scans.
An international team led by Ulrich Welp at Argonne National Laboratory in Illinois, US, has come closer to producing a beam of terahertz waves or 'T-rays' that could revolutionise airport security and medical scans.
Persuading normally independent quantum junctions to work together has created this.
The T-rays are sandwiched between infrared light and microwaves in the electromagnetic spectrum. Many researchers are trying to use them because, like microwaves, they can pass through many materials such as clothing, but provide much higher resolution images.
Josephson junctions are made from a sandwich of superconducting material with an insulating filling. They can produce terahertz waves when voltage applied to the superconductors makes a "current tunnel" through the insulating layer.
Welp and colleagues made hundreds of junctions work together, creating a beam of laser-like terahertz light with 10,000 times more power (about half a microwatt).
The team used a high-temperature semiconductor called BSCCO, which naturally contains stacks of Josephson junctions in its structure. It comprises of super-conducting sheets, a couple of atoms thick, separated by 1.5 nanometer-insulating gaps.
The usually unruly junctions were tamed with a carefully chosen voltage applied across the superconductor. That created a stationary electromagnetic wave that coordinated the junctions' actions.
"That was the trick. People were never able to synchronize all these junctions before," says Welp.
By using different size crystals, they were able to fire T-ray beams of 0.36 to 0.85 terahertz, covering about a third of the terahertz gap. They aim to decrease the gap further by making their crystals narrower, Welp says, and also plan to increase the power output.
The new study is a significant step forward, says August Yurgens of Chalmers University of Technology in Gothenburg, Sweden.
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