Applications – including medical and industrial imaging, and chemical detection – depend on small, power-efficient sources of terahertz rays, and the standard method for producing them is said to involve a bulky, power-hungry, tabletop device.
The researchers' design is a new variation on a device called a quantum cascade laser with distributed feedback. Until now, however, the device emitted radiation in two opposed directions. Since most applications of terahertz radiation require directed light, that means that the device squandered half of its energy output.
To counter this problem, the team found a way to redirect 80% of the light that usually exits the back of the laser.
"We increased power without designing a new active medium, which is pretty hard,” said graduate student Ali Khalatpour.
In the waveguide, materials are arranged so that the application of an electric field induces an electromagnetic wave along the length of the waveguide.
The group cut regularly spaced slits into the waveguide, which allow terahertz rays to radiate out. The slits are spaced so that the crests of the waves coincide only along the axis of the waveguide. At more oblique angles from the waveguide, they cancel each other out.
The researchers then simply put reflectors behind each of the holes in the waveguide, a step that they claim can be seamlessly incorporated into the manufacturing process of the waveguide.
The reflectors are wider than the waveguide, and they're spaced so that the radiation they reflect will reinforce the terahertz wave in one direction but cancel it out in the other.
The device has been selected by NASA to provide terahertz emission for its Galactic/Extragalactic ULDB Spectroscopic Terahertz Observatory mission to conduct spectroscopic measurements of oxygen concentrations.
