What is Terahertz imaging? Use of Terahertz imaging in reading closed books?

Terahertz Imaging can be used to read Closed Books which are Old

     

      Terahertz imaging is a technology which makes use of the Terahertz frequency which ranges from 0.1 THz - 3 THz and lies between the microwave and infrared frequencies. Terahertz frequency is able to see through many materials which are blocked by visible and infrared spectra which make it beneficial to be used for terahertz imaging. 
  

     Thus, compared to the microwave radiation or the conventional X-rays, it is able to achieve better spatial resolution which is required for rendering quality imaging with the help of T-rays or terahertz frequency range.

     Now, if we want to know the depth of the mine which we dug, we would send laser in the deepest point and then measure the time it takes to travel back to the source. As we know the speed of light, we can calculate the depth. The same is with the SONAR, the ship's send sound waves in the water and measure the time it takes to come back, thus calculating the depth of the sea.
  
     Same is in the case of Terahertz imaging. The beams are send through the camera and after colliding with the material, they bounce back and the absorbed and reflected radiation is measured. 

     Terahertz Imaging was originally used in search of petroleum reserves and scanning of luggage at the airport which cannot be seen through x-rays. But now it is mostly used in restoration of art. In fact, researchers at Massachusetts Institute of Technology(MIT) have developed a Terahertz camera that can read through closed books.

Terahertz Imaging Camera
Image Source: Barmak Heshmat

     
     The researchers specifically focus on Time domain spectroscopy (TDS) which sends short pulses of terahertz light (which ranges from 0.1 THz - 3 THz) and measure the radiation which is reflected. The terahertz radiation has an ability different from others which makes various chemicals produce different frequencies of their own. This helps in differentiating between ink and paper and further detects individual words and words on pages of a book.

Image Source: Camera Culture Website

Image Source: Camera Culture Website

      
      The camera was able to read 9 pages of a book in 2016. Yes! You can read 9 pages of a book without even opening it. The researchers are very confident about the technological development in these field. Now, you might wonder why would anyone want to read a book without opening it? People are not that lazy!

     The reason is, there are many such manuscripts, novels and books that are found in historical research and are very delicate, that they will get damaged by the slightest touch or their page might tear while turning. In this case, the terahertz imaging is very beneficial.

     While concluding I will just say that, Terahertz imaging is a great technology that has many applications from airport security to restoration of art. With the help of it, who knows in future we might even be able to read a whole novel without damaging it.