Terahertz spectrometer allows unopened books to be read

Called a terahertz spectrometer, it managed to clearly read nine pages and could see writing on up to 20.

The system developed by the team looks like a cross between a camera and a microscope and works by directing ultrashort bursts of terahertz radiation at stacks of paper.

Some of it is absorbed by the paper, and the remainder is reflected back. The signals that bounce back are then analysed with algorithms that can discern individual letters.

Terahertz waves are a type of radiation situated on the electromagnetic spectrum between microwaves and infrared light.

The technology could one day be used by museums to scan the contents of old books too fragile to handle or to examine paintings to confirm their authenticity or understand the artist's creative process.

"We were very excited because we didn't think we would be able to see as deep as we did," said Barmak Heshmat, an MIT research scientist.

While the device is still a long way from actually scanning an entire book, Heshmat said the team is already talking with the Metropolitan Museum of Art in New York about using it to inspect some of its artworks and antique volumes.

The technology could also be used in industry, to see whether there are cracks or other defects beneath the paint on an aircraft part, for example.

Heshmat said that for now, broader uses would be limited by the cost of the device, which runs about $100,000 (£75,000).

In the study, the stack of paper had no cover, but Heshmat said he is confident the system could see through one.

Heshmat said the system works much better than X-rays, which are currently used to scan documents and paintings but entail harmful levels of radiation.

With X-rays "you won't be able to read the pages unless the ink is written by some metal like silver or gold", he said.

"But with our system, because it uses a different part of the electromagnetic spectrum, it can identify many other chemicals, so it can contrast between the blank paper and the part that has ink."