"We found a way to get around the water moisture problem," said Lui, and use terahertz waves for long distance scanning.
Military and homeland security officials are funding much of the T-ray research, including the RPI study, because T-rays can sense explosives and drugs as well as penetrate clothing, paper or other thin materials. T-rays also do not produce harmful, ionized radiation like X-rays.
Since T-rays are very difficult and expensive to produce, they occupied a little used part of the electromagnetic spectrum between infrared and microwave radiation until the last few years.
Since 1995, however, scientists have found ever cheaper and easier ways to produce T-rays, but they haven't quite worked out all the kinks yet.
Water molecules absorb T-rays and weaken them after only a few inches, making any kind of long-distance scanning, however desirable, extremely difficult. The RPI scientists found an ingenious way around the water vapor problem.
Rather than using terahertz waves to transmit data, the researchers instead employed them to detect information. The team then used other wavelengths of light, which are not weakened by water vapor, to bring that information back.