Can computers read through a book page by page without opening it?
cameraculture.media.mit.edu
cameraculture.media.mit.edu
Also, what are the laws of the US government applied this to reading our letters. Our mail is protected by law from opening, but what if they aren't physically opened?
I think I saw this stuff at the International Spy Museum in Washington DC; it was a much more interesting museum than I expected.
[1] http://www.produktinfo.conrad.com/datenblaetter/600000-62499...
Up until now these would have been specific and targeted attacks where the benefit was worth the effort of the task, with little effort required they will have no reason not to.
Only in democratic countries you can expect some privacy.
Zomega was one of the few companies with a true terahertz system, at 2THz, or 0.006in wavelength. Other "terahertz" products seem to be around 100GHz, which is much easier to reach; there are 77GHz automotive radars.
Zomega systems had already been used to image hidden layers in paintings, so looking into a stack of paper wasn't a big stretch. This new paper is mostly about a data reduction technique.
Overview of terahertz technology.[2]
[1] https://web.archive.org/web/20151220072732/http://z-thz.com/ [2] http://spectrum.ieee.org/aerospace/military/the-truth-about-...
The ultra-short laser pulse can be generated through purely-optical means. You have a laser pulse traveling around a cavity. Due to a combination of non-linear optical effects, each round-trip tends to shorten and concentrate the pulse. The resulting pulses can be much shorter than what's achievable with electronic generators.
All that's left is thought scanning and then we will think about rethinking passwords.
Still mostly science fiction, but plausible.
Could this technique also be useful for crystallography, or electron microscopy?
I don't want to say it's impossible, but I think you'd have to improve the capabilities of our instruments by about four orders of magnitude, which means you would have to invent several new major technologies.
Maybe if you digitize the time-domain pulses using some kind of controlled nuclear reaction? Electronics are far too slow (although I don't really understand why, so maybe that can be fixed). X-ray-stimulated nuclear reactions are going to be tricky to get to happen at all, much less to chain together into computational circuits, although in that case maybe you can use α particles or neutrons to carry the information around between the computational elements, simplifying the task somewhat.
It seems like, however you manage to measure it, the quantization of the radiation is going to pose really significant problems to measuring its amplitude accurately as a function of time, but maybe you can get around that by repeating the pulses a lot of times. But you'll need to make sure that you're emitting pulses of the same shape, rather than just pulses with a similar frequency spectrum and envelope but varying relative phases among the frequencies.
On the other hand, if you just want to measure the time-of-flight for X-ray wavepackets to sub-picosecond precision, without worrying about the time-domain waveform within the packet, I don't think that gets any harder or easier depending on the "carrier frequency" of the wavepacket — X-rays should be just as easy as terahertz light. You do need a few terahertz of bandwidth, so you aren't going to be able to do this with bursts of gigahertz microwaves.
X-rays' interaction with the material you're trying to image might be less or more convenient; their cross-section for backscattering is pretty small, but maybe you could scan the book from different angles and use total internal reflection to find interfaces between materials in the book with different refractive indices. This would also reduce your requirements for time-domain precision down into the hundreds of GHz range, which is a lot easier to deal with.
Terahertz TDS already samples at frequencies beyond the capabilities of bare electronics (look at my other comment on this story).