From Space Shuttle to Da Vinci 'T-Ray' Technology Strips People and Frescoes

Terahertz scanners have already been used at NASA, the European Space Agency, and at airports to look beneath people's clothes for concealed weapons. Now researchers are turning "T-rays" on church walls -- and hoping to revolutionize art history in the process.


No doubt Q is tinkering away at it right now. By the next film, at the latest, he will hand James Bond a palm-sized device. Agent 007 will handle it very gently for a bit and raise an inquisitive eyebrow. "That's a terahertz scanner," Q will say. "It'll find everything, even anthrax spores in suspicious envelopes. Or it can make weapons hidden beneath clothes visible." Then 007 will raise the other eyebrow and point the scanner at Q's attractive laboratory assistant, who will then appear on the device's display -- naked. "Hey!" Q will complain, bristling scornfully.

In reality, terahertz rays are not so easy to handle, though they are increasingly popular among customs officials and homeland security agents. Although they lie somewhere between infrared radiation and microwaves along the electromagnetic spectrum, these rays have yet to be put to any commercial use. Existing detection devices can barely pick them up, and the development of terahertz emitters is still too expensive for wider application.

From Airports to NASA to Art History

In 2005, the first test devices were set up in select airports in order to "X-ray" suspicious passengers for weapons and explosives. Unlike X-rays, terahertz rays are harmless from a health standpoint. They are "non-ionizing," meaning that they do not have enough energy to jostle atoms apart and damage body cells the way X-rays do. The rays have already been used by the European Space Agency in a large-scale project which measures the Earth's surface temperature. And NASA regularly uses "T-rays" to check for damage to the tanks of the space shuttle because the walls of the tanks are buried under thick layers of insulating foam.

A team from the University of Michigan has been working to develop applications for these waves. The researchers have seized upon an application that is peaceful, clean, beautiful and of cultural value: old wall paintings. Over the course of time, countless colorful images on the walls of churches or palaces have been painted or plastered over. Until now, there's been no way to detect these images, rendering them as good as lost.

But initial tests have shown T-rays are able to detect penciled sketches under layers of both paint and plaster. Come March, the Michigan team is taking their show out of the lab and onto the road. Working with specialists from the Louvre, the team will pay a visit to the Church of St. Jean Baptiste in Vif, France. Frescoes from the 13th and 14th centuries were recently discovered under five layers of plaster on the walls of the 13th-century church. After their first attempts to expose the frescoes, the conservators gave up. Now they are awaiting the help of the physicists from Michigan.

"Terahertz is a strange range in the electromagnetic spectrum because it's quasi-optical. It is light, but it isn't," Bianca Jackson told photonics.com, which follows developments in the optics industry. Jackson is writing her Ph.D. dissertation on terahertz and recently published the results of her research on color in the periodical Optics Communications.

After a Lost Da Vinci

The team's T-ray system was developed at Picometrix, a company based in Ann Arbor, Michigan. It sends ultra-fast laser pulses to a semiconductor antenna, which in turn emits pulses of T-rays. The rays then penetrate the plaster, and a certain proportion of them are reflected back from the underlying layers. The type of material beneath the plaster is determined by how quickly the rays are reflected and by how much energy they have retained. Paints of different colors have their own characteristic signals. A receiver measures the reflected energy, and the data is used to determine the image hidden beneath the top layer, Jackson told photonics.com.

Of course, for their initial experiments, the young physicists didn't have any wall paintings at their disposal. Instead, they drew a picture of a butterfly with a pencil and covered it over with various layers of different-colored paint. Whether through black, white, yellow or red paint, the T-ray system was able to detect the butterfly through the layers covering it.

The device had no problem, even when the plaster got as thick as four millimeters (0.16 inches). In doing so, it far surpassed all previous methods of detecting even the thinnest layers of paint. If the T-ray system passes the test in Vif, too, it could revolutionize art history. "In France alone, you have 100,000 churches," Gèrard Mourou, Jackson's dissertation adviser, told photonics.com.

The little butterfly was just the beginning. Jackson's dream is to help search for Leonardo da Vinci's lost work "The Battle of Anghiari." For generations, art historians have frantically searched for the unfinished painting. They suspect that it might lie behind a wall painting of Giorgio Vasari in Florence's Palazzo Vecchio.

When Jackson speaks about the lost Da Vinci work, you can hear the excitement and anticipation in her voice. Engineer Maurizio Seracini is currently examining the suspected layers with a neutron scanner. "We're trying to make contact with Seracini to see if he'd like to cooperate," Jackson told SPIEGEL ONLINE. "We'll surely get a lot further with terahertz than with neutrons."

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