Terahertz radiation exists at the edge of the far infrared part of the spectrum, near microwaves. This range of frequencies is of great interest to researchers the world over because only water and metal blocks it. This property makes terahertz incredibly useful for communication and sensing devises as the radiation does not adversely affect the human body. From medicine to security and communication, terahertz technology would have a great impact. Before that can happen though, researchers have to be able to control the waves.
Rice University researchers have recently devised a terahertz polarizer that operates on frequencies from 0.5 to 2.2 THz. This is huge compared to other polarizers. The new design utilizes nanotubes that will other block or allow transmission of the radiation based on an external electric field. A nanotube polarizer had been tried before, but was only able to block 30-50%, which isn’t enough. To fix this the researchers made it thicker. The result is a polarizer that can switch from allowing 100% of a terahertz signal through, to blocking 99.9%.
Further improvements to the polarizer can be made, but they will require overcoming an issue all nanotube researchers are having. When nanotubes are grown the sample includes both semiconducting and metallic nanotubes. Only the semiconducting are useful in the polarize, but there is currently no efficient way to either sort out the types of nanotubes, or simply produce one kind instead of both.