Metamaterials could bring cheaper T-ray scanners: "As the terahertz waves emerge from the laser, some are diffracted sharply through 90 degrees and are converted into waves called surface plasmons, which ripple vertically down the metamaterial. The grooves in its surface trap clusters of these plasmons, prompting them to radiate their energy as T-waves.
The spacing between the grooves is chosen so that the terahertz emissions constructively interfere with each other. As a result, the beam is relatively tightly focused in the vertical direction, diverging at an angle of 10 degrees, rather than the standard 180 degrees. "This leads to the efficient collection and high concentration of power without the need for conventional, expensive and bulky lenses," Capasso says."