The Times Online has a nice summary of a new technology that uses terahertz to detect anomalies for airport security:

The system can be linked to a computer so that it can automatically scan anyone passing and alert its human operator to anything suspicious. Clive Beattie, ThruVision’s chief executive, said: “Acts of terrorism have shaken the world in recent years and security precautions have been tightened globally. The T5000 dramatically extends the range over which we can scan people.”

[…]

The technology works by detecting and measuring terahertz waves, or T-waves for short. These are a form of electromagnetic radiation, emitted by all people and objects that lie between the infrared and microwave parts of the spectrum.

A quick search reveals that similar systems have been in use for some time. For example, a mail scanner was tested in 2003:

At the heart of the Japanese system is a compact and tunable optical parametric oscillator (OPO) that emits terahertz waves. The OPO is made from a nonlinear crystal (MgO:LiNbO3) that is pumped by a Q-switched Nd:YAG laser. It emits terahertz radiation that is tunable between 1 and 2.5 THz.

Terahertz waves of several different frequencies are scanned over the envelope and the transmitted radiation is picked up by a pyroelectric bolometer and analyzed by a computer.

Apparently the mail does not naturally emit T-waves, but people do. I don’t suppose it hertz to be scanned with T-waves, eh?

At some point there will be enough development and advancement in spectrum sensor technology that airports will have the capability of profiling people entering, coupled with surveillance, so the inefficient “choke points” will become obsolete. In other words, just like astronomers today use T-waves to study the sky, airport security staff may someday monitor from above the space people travel through.

One thing that will not go away, like astronomy, is the need for human operator/analysis to accurately interpret the results.