This is another piece from nature.com on Tetrahertz scanner.

British forensic scientists have developed a new scanner that could spot concealed drugs and explosives in packages or under clothes. They hope that the device, which uses 'terahertz' rays to peer through a wide range of materials, could become a fixture in mail-sorting offices, police stations or mobile forensic labs.

Terahertz waves, which have a wavelength between those of microwaves and infrared, can permeate a wide range of materials including paper, fabrics, plastics, wood and human tissue. But they are blocked by many drugs and explosive compounds, making them potentially useful for security or forensic scanning.

The device is "the size of a ski-boot box", says Malcolm Dunn of the University of St Andrews, UK, who presented the scanner at a forensic technology meeting in London on 30 March. "And we're hoping it could ultimately become man-portable."

The idea of using terahertz waves to scan for drugs and bombs is not new: in 2001, a team at Japan's RIKEN laboratories unveiled a terahertz generator with such an application in mind. But their device was huge and cumbersome, because the way they created terahertz waves required a clunky array of lasers.

Terahertz radiation lies in a narrow band of the electromagnetic spectrum, squeezed between microwaves and infrared light. Producing these waves is not easy. One way to do it is by firing a 'pump laser' into a material known as a parametric generator, usually the chemical lithium niobate. Changing the angle at which the beam is passed through the material alters the frequencies produced, allowing the output to be tuned.

Dunn and his team created a compact terahertz generator by installing the parametric material inside the machinery that generates the pump laser, rather than outside. This also makes the device more efficient, they say, as less strength is lost from the laser source.

Is that cocaine in your pocket?

Terzhertz rays from the scanner would be blocked by any concealed drug or explosive compounds, but would pass straight through clothes or packaging. Dunn and his colleagues have already successfully used it to spot compounds similar to heroin and cocaine stuffed inside envelopes. They are now considering how best to obtain government approval to study the real thing.

Detecting drugs in real situations will require careful calibration of the machine, says Giles Davies of the University of Leeds, UK, who has been studying the terahertz spectra of a range of drugs and explosives. Precise data on how these compounds absorb terahertz radiation will be crucial in spotting whether a traveller is carrying cocaine, or just washing powder, in his luggage, he says.

On the street, drugs can take many different chemical forms, Davies adds. Cocaine, for example, comes in different forms such as 'freebase' cocaine, which is smoked, and cocaine hydrochloride, which is typically snorted. Furthermore, the drug is frequently cut with laxatives, baking powder or artificial sweeteners, all of which change its chemical signature. Officials would also like to spot precursor compounds to drugs, such as ephedrine hydrochloride, which is used to make amphetamines and ecstasy.

It will be years, rather than months, before the scanner becomes commonplace in forensic labs or post offices, Dunn says. He and his team are now seeking industrial backers to build a prototype that can be tested in the field.