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Visible Light 'X-Ray' Sees Through Solid Objects
disco_tracy writes "Some day we may not need X-rays to see inside people, thanks to a new way to decipher light that passes through opaque surfaces. Normally visible light becomes too scattered to detect after passing through opaque surfaces. But scientists in France have developed a way to reconstruct images from light passing through such surfaces by deciphering just how the material makes the light scatter. In the short term the research will help improve the strength of telecommunications signals and fiber optics cables, but years from now the technology could supplement or even replace traditional ultrasounds for baby imaging and X-rays for weapons detection at airports."
This will make the "xray" threads on /b/ waaay more interesting.
There's no -1 for "I don't get it."
How does visible light make its way through an opaque object?
I want to delete my account but Slashdot doesn't allow it.
How does visible light make its way through an opaque object?
I know you aren't supposed to read TFA, but ""It's like putting a flashlight behind your hand," said Sylvain Gigan... "You cannot see an image, but you can still see a faint glow.""
No. Reading is useless without understanding. The OP was correct in asking. Your hand is not opaque, it is translucent.
"National Security is the chief cause of national insecurity." - Celine's First Law
I know you aren't supposed to read TFA, but "'It's like putting a flashlight behind your hand,' said Sylvain Gigan... 'You cannot see an image, but you can still see a faint glow.'"
I think it would help if TFA included an actual example image, and not just a photo of someone holding their hand up behind a shower screen and a note to the effect that the actual technology might produce images sort of like that one.
"...always new atoms but always doing the same dance, remembering what the dance was yesterday." -Richard Feynman
Not likely (in the US at least). Kyllo V United States established that using IR to peer into a home requires a warrant, and that's a pretty strong precedent. A key issue of the case was that using IR didn't even need to penetrate the house (it just "recorded" what was being emitted) and yet was STILL not allowed without a warrant. Anything that "peers in" will be just as illegal.
I live in constant fear of the Coming of the Red Spiders.
Nowadays, "illegal" doesn't mean you can't do it -- it's just not admissable in court.
You can get your last dollar they still do it, but then need to come up with a pretense for anything involving the courts.
Remember, they can now slap a GPS device onto your car with absolutely no court oversight. Just imagine all of the illegal things they do and cover with sealed court proceedings.
Lost at C:>. Found at C.
The idea is that you send light against an opaque medium, the photons getting blocked or scattered is a statistical process. Some of them, simply as a matter of probability, "sneak through" in a straight line.
To get around the low probability, you use a strong light source, modulate it (if you modulate the light, you can pick it out with a tuning circuit, so that you can screen out background light), and then average over a long period of time.
Eventually, you get enough ballistic photons through that you can map out an image.
Ultrasound is for listening to sounds inside the body, such as the faint heartbeat of an unborn human.
No it isn't. Ultrasound is ultrasonic, by definition. (Higher frequency than normal sound.) Ultrasound is often used for imaging; the resulting images are called sonograms. Ultrasound can detect heartbeats through movement (Doppler shifting the ultrasound waves). It's not for listening to normal sound waves originating from inside the body. That's just a stethoscope (or fancier variant thereof).
It just so happens that your object here is only MOSTLY opaque. There's a big difference between mostly opaque and all opaque. Mostly opaque is slightly transparent. With all opaque, well, with all opaque there's usually only one thing you can do.
It's called Ballistic light.
Eventually, you get enough ballistic photons through that you can map out an image.
And if you get the light strong enough, you resolve the opacity issue permanently, once the smoke clears.
A sonogram is the image produced by an ultrasound machine. Ultrasound imaging is called "ultrasonography."
Listening to sounds within the body is called auscultation.
Eventually, you get enough ballistic photons through that you can map out an image.
Physicists don't actually use terms like "opaque" very often. We are more likely to talk about material that is "highly absorbing" or "highly scattering". The human body contains lots of both.
One area where people have tried to apply this is in optical mamography: women's breasts are primarily fatty tissue that is highly scattering but very weakly absorbing, so you get a surprisingly large fraction of transmitted light. You have to do a huge amount of processing to deconvolve the scattering kernel, but when I worked in the area in the late '90's it was getting close to useful.
For people reading this who are female or who have wives or girlfreinds willing to go along, go into a dark room and hold a flashlight under your (partner's) breast. You'll be amazed by the amount of veinous structure and whatnot you can see. Squeeze the breast flat to get more detail. Insert joke here about how now you're in a dark room with a woman who has at least one breast exposed so you know what comes next...
Very athletic women with smaller breasts may not see much: the chest muscles are highly absorbing and any any photon that scatters into them is lost.
High-speed computation is making visible light a more useful medium of detection all the time, and the work described in TFA is an interesting step along the way.
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