Reading through closed books

[music] Barman: Ten years ago there was a group at MIT which showed that you can look through a closed envelope with terahertz waves. And that was really inspiring to me and I was like hm, if you have the time resolution of the terahertz spectrometer, now you can actually look deeper into multiple pages. I was really curious. I wanted to know how deep you can read through a closed book because nobody has tried that.

In order to read through a closed book you have to do 4 things. First, you have to have a radiation that goes through the paper. So the paper has to be slightly transparent in this frequency range. Second, you have to have the time resolution to distinguish between different pages. Femto-photography was a project that opened the gateway to numorous projects that we have done here in our group. With advancement in the time resolution we were able take a look at objects that have much finer details. With this time resolution we can actually separate the pages. We can look at some very very small objects. The pulse that you send in is going to be reflected by each of these air gaps by each page. And we try to separate the pulses that actually from this air paper boundary compared to the noise that is coming from the rest of the sample.

Third, you have to have the spectral information of different inks – for example, the ink should be visible in that range of frequencies. And the fourth one is recognizing the characters themselves. There’s a shadow of different letters onto of the next page. So the algorithm has to be able to recognize the characters although some part of the letters is missing. So right now we can see through 9 pages of the closed book because we don’t have enough power and signal to noise ratio. And with advancement of technology that would improve significantly so we can see deeper through the book. One of the applications is studying or doing inspection on antique documents. It’s like an ancient book or whatever and you cannot even touch it to open it and see what’s inside. You can get some information about the layers with X-ray but you cannot get information about the content like what is written in this book.

Our ultimate mission in Camera Culture at MIT is to make invisible visible and time resolution is an essential part of doing that. I really like reading from the screen but there are some of the books that I have to have. For example Physics of (the) Impossible from Dr. Michio Haku. And the reason for that is that it’s both inspiring in terms of like science and also in terms of how capable humans can be with technology..

As found on Youtube