janrinok writes:
Science Daily is carrying a story about a recently developed, ultra-thin light detector working in the infra-red (terahertz) band. This discovery, made at Vienna University of Technology, now opens up the possibility of integrating a light detector for terahertz radiation into a chip. From the report:
"With conventional fabrication methods, large arrays of such detectors can be built," Professor Karl Unterrainer explains. They do not take up much space: Layers with a thickness in the order of magnitude of nanometers are enough to detect light -- the detector is more than a thousand times thinner than the wavelength of the light which is being detected.
"Ultra-thin layered semiconductor systems have the great advantage, that their electronic properties can be very precisely tuned," says Unterrainer. By selecting suitable materials, by tuning the thickness of the layers and the geometry of the device, the behaviour of the electrons in the system can be influenced. That way, quantum cascade lasers can be built, in which the electrons jump from layer to layer and emit a photon with each jump. Also, light detectors can be created, with a selective sensitivity to one particular wavelength.
The problem, however, is that quantum physics prohibits photons with a certain directions of oscillation (polarization) from interacting with the electrons of the semiconductor system. Light which hits the layered surface head-on, cannot influence the electron in the semiconductor. Therefore a method is required to rotate the polarization of the incident light, so that it can be detected in the semiconductor layers.
(Score: 5, Informative) by ikanreed on Monday March 31 2014, @10:06AM
http://en.wikipedia.org/wiki/Quantum_cascade_laser s [wikipedia.org]. Applications seem to center on spectrography(A mobile spectrographer would be one big step closer to a tricorder), and since this tech is also good for modulatable wavelength detection, it also seems useful for EM scanning.
On the other hand, if they haven't solved the problem of sending that data to a computer, it's kinda useless.
(Score: 5, Informative) by bd on Monday March 31 2014, @11:30AM
No, this device is not for spectroscopy.
While spectroscopy is an application of QCL's, you usually use them for the mid-IR. One problem with QCL's is temperature. For the IR you can get away with a couple of peltier elements. For THz applications, you have to cool them to cryogenic temperatures. Therefore, you usually use different THz sources.
This is a fundamental problem of QCL's, as kT at 300 K is at about 26 meV and a transition of 10 THz is only about 40 meV. Therefore, you have to cool them significantly for usage in the THz region. In the case of the device from the article, they cooled it to 5 K, and the device doesn't work at all at more than 150 K.
The device in question is intended as a pixellated sensor, for THz imaging. Up until now, such sensors are available for the sub 1 THz region, and work reasonably well at 300 GHz. They work by electrical down-conversion using high-speed transistors and an antenna array. But there is no pixellated sensor that I know of in the 10 THz region that works well.
The trick with the device is that they use a normal quantum cascade structure, that would absorb light that enters at the corners of the device, and use a meta-material to change the light that comes from above into the right polarisation to be absorbed by the QCL structure. Therefore, they can build a pixellated QCL array.
A drawback will be that such a device will be extremely expensive to produce and that there is not yet a good practical application for THz imaging. For most problems, there exists another imaging technique that yields better results for less money. I did recently hear that a certain kind of plastic material can be inspected for defects using THz radiation in a way that is better than all other known methods, so there might be an industrial imaging application in the near future. Everyone is But that is only hearsay at this point.
The science daily article is actually good btw, nothing in it seems to be wrong. That is seldomly the case with science reporting!
(Score: 2) by mhajicek on Monday March 31 2014, @02:13PM
I thought the quantum cascade laser was the thing in Half-Life that punched a hole in the fabric of the universe...
(Score: 2) by ikanreed on Monday March 31 2014, @05:00PM
All you gotta do is add some resonance, and remove some laser. Sounds easy.
(Score: 3, Interesting) by VLM on Monday March 31 2014, @11:05AM
To answer the meta question of why, this is a slight simplification but all organic compounds are dyes, just maybe not in visual light. In IR especially you get a real rainbow. So you can identify organic chemicals using IR. Cool. But the minimum required concentration or minimum sample volume depends on the brightness of the IR light or how sensitive your IR detector it.
Like most technologies you can use it for good or evil. Maybe OSHA can force the installation of environmental detectors just like smoke detectors to sense spills for evac. Or if it gets really cheap, smoke detectors could tell the difference between "burned cookie smoke" and "wood smoke" and respond accordingly. Or we can get all dark and shine a laser at oncoming traffic to continuously breathalyze drivers until you catch a drunk, or
(Score: 1) by Ethanol-fueled on Monday March 31 2014, @11:56AM
Or being sniped by a laser. That was your joke, right?
(Score: 2) by VLM on Monday March 31 2014, @12:06PM
Unfortunately, kind of ironic given your username, the most likely use of a remote ethanol detecting laser by the local pigs would be gaining probably cause for their local DWB campaign. So lase non-white people driving in my city till you get an ethanol hit, then pull them over for having filled theit gas tank with E10 gas or wearing cologne or using mouthwash, and give them the usual talking to about why "they" are visiting "our" little city. So thats what I was aiming at.
(Score: 2) by Nerdfest on Monday March 31 2014, @12:04PM
Can someone explain why the oscillating protons can't interact with the semiconductors? I'm guessing it's because they're oscillating in a specific, therefore known direction, but that doesn't make sense as they should still be able to interact.
(Score: 3, Funny) by TrumpetPower! on Monday March 31 2014, @12:06PM
...and, once somebody creates an ultra-light thin detector, they can sell it to fashion photographers for insane amounts of money with the promise that they'll be able to recoup it on lower Photoshop artist expenses.
b&
All but God can prove this sentence true.