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Mastering Light
thyristor writes "'Researchers at MIT document the ultimate control over light: a way to shift the frequency of light beams to any desired colour, with near 100 per cent efficiency. This technology could revolutionise a range of fields, from turning heat into light, or even into prized terahertz rays - which hold great promise for medical imaging. It could also make it possible to focus a wide range of frequencies into a narrow band, make devices such as light bulbs and solar cells more efficient, and help to keep optical telecommunications networks moving.' These are probably the most exciting results in photonics in the last decade."
stop making light of real progress
Joannopolous was also involved in the development of the "perfect" dielectric mirror, which was mentioned here before.
This would actually be pretty cool for the average DJ or night club, since traditional filters are so inefficient, and thus cause you to use higher wattage light, and more heat (and more AC to deal with it). This could make club lighting more attractive, more sophisticated and more varied.
:-)
After all, if science can't help drunk/horny/single people get laid, what good is it?
Tequila: It's not just for breakfast anymore!
I flat panel displays will no longer need separate reg, green and blue pixels. They could just have uniform pixels which could produce light in any shade required. Should be good for higher resolution displays, greater colour depth. But might mess up things like sub pixel rendering.
http://grc.com/cleartype.htm
"Taligent is still pure vapor. Maybe they'll be the last who jumps up on Openstep... "
The approach is destructive of the crystal used for filtering the light, although they hope to be able to use sound waves in the future. Due to the distorion of the crystal lattice structure required, even sound waves may wind up breaking the crystal (remember the old memorex commercials with the singer breaking a crystal wine glass). The approach is very interesting, but there still are some serious design issues that they need to address, otherwise, it will be tough to deploy this for applications such as optical repeaters or switches.
Well, with such a frequency translator, we can all imagine all the goodies and baddies that can be made with it. One of them is a cloaking devices, efficient power sources, phase weapons...
Imagine changing harmless light from light bulbs into a focused gamma rays or worse !
- Generate low-frequency (LF) pulse travelling into crystal.
- Apply shock wave to turn crystal into frequency shifter.
- Wait until LF pulse is shifted to higher frequency and emitted from crystal.
- Allow time for crystal to relax to original properties by allowing the shock wave to dissipate.
- Repeat for as long as necessary/desired.
Now, this may or may not create any really usable stream of pulses, but I believe that you would be able to shine a (pulsed) red light in and get a (pulsed) blue light out. Whether the pulsing could be controlled sufficiently to prove useful in optical switching or other applications is yet to be shown.As for the number of wavecycles being equal, I wonder if this is already observed. It would make sense (if the number of wavecycles is conserved) that the resulting higher frequency pulse would be shorter in duration than the incoming lower frequency pulse, due to the relation among the speed of light/frequency of light/duration of pulse.
I think the summary's mention of "near 100% efficiency" is misleading. It all depends on how wide your definition of the system is. Yes, technically the material itself appears to be highly efficient, but that's discounting all the energy used creating the shockwave necessary to give the material these properties.
A fascinating discovery, yes, but a miraculous way to convert energy to suit our needs it is not.
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Reading the article it seems that the light frequency is altered for only a short time, the time during which the shock wave passes through the crystal.
So you put through another shock wave and another and another and another...
You will get the same number of peaks and troughs out, but those that have bounced back and forth a bit (and thus got Doppler shifted) will come out later, having travelled further, and shifted. This technique stretches the light pulse.
So, (asciiart time!) you could put in pulses of green and get out continuous red:
S S S S
gggg gggg gggg gggg
rrrrrrrrrrrrrrrrrrrrrrrr
[View it in a fixed-width font, it'll make sense I promise]
Each green pulse g has been stretched by the shockwave sent at each S and turned to red light r, filling the time for pulse + gap.
Justin.
You're only jealous cos the little penguins are talking to me.
Not much more information than in the article, but here's the abstract. This is pretty similar to Bragg scattering, which is a well known effect that uses sound waves to upshift the frequency of light. Current Bragg cells are very inefficient and are limited to small shifts in frequency. A high efficiency Bragg cell capable of shifting frequency by a large amount would be extremely interesting.
From Physical Review Letters.
Color of shock waves in photonic crystals
Evan J. Reed, Marin Soljacic, and John D. Joannopoulos
Unexpected and stunning new physical phenomena result when light interacts with a shock wave or shock-like dielectric modulation propagating through a photonic crystal. These new phenomena include the capture of light at the shock wave front and re-emission at a tunable pulse rate and carrier frequency across the bandgap, and bandwidth narrowing as opposed to the ubiquitous bandwidth broadening. To our knowledge, these effects do not occur in any other physical system and are all realizable under experimentally accessible conditions. Furthermore, their generality make them amenable to observation in a variety of time-dependent photonic crystal systems, which has significant technological implications.
Physics, Cosmology and
It's not the joke, it's the frequency of them.
"Times have not become more violent. They have just become more televised."
-Marilyn Manson
Right now you can buy AOTF cristals. It is a bit similar, but works as a filter (Acousto Optic Tunable Filter). What it does is bend off one specific wavelength of light based on which ultrasound you beam through it. By sandwiching a AOTF crystal between a piezzo and an absorber, you get a filter which you can control with a waveform generator. Brimrose will sell you a spectrometer that can scan 16,000 wavelengths per second for a ridiculously cheap 100,000$. Downturn is it throws all other wavelengths out meaning you still need a 35 Watt halogen lightsource to measure anything. If you could "recuperate" or shift the other wavelengths then you could use LED's as a light source and have a completely solid-state spectrometer with > 30000 H MTBF. You would use less power, produce less heat, make it smaller, send it to Mars,....
10 ?"Hello World" life was simple then
This certainly sounds like an excellent advance in the field.I have been aware of interesting work with shock waves in other materials, for example, to create hydrogen metal, but it wouldn't surprise me if these claimed results were valid.
There are a couple of problems with the article and its claims, however:
I hope for the best, but remain sceptical; let's hope these new shockwave effects become easier to generate and exploit!
IAAP (I am a Physicist) and the effect is pretty simple. I think anyone should be able to understand it if it is explained properly.
"Doppler Shift" is a phenomena you are already familiar with. Consider a car honking its horn as he drives by at freeway speeds. As he approaches, the sound is heard at a higher frequency. As he passes by, the frequency shifts, and as he is leaving, the frequency is lower than normal.
Light is like sound in that it is a wave and has a frequency. Let's examine light from high to low frequencies. X-Rays are light at extremely high frequencies. Ultra-Violet light is just above the visible light range. Then we get into the rainbow - blue, then green, then red. Next is infra-red light -- light just below red in frequency. Travelling farther down, we start to reach the radio band. Below that, the frequencies are so low that it no longer is light anymore, but more like a slowly shifting magnetic or electric field.
The Doppler effect works for light as well. The problem is you or the object emanating the light has to be travelling near light speeds to see any noticeable effect. We call this "redshift" in astronomy, because stars seem to be travelling away from us, and so the light emanating from them is lower in frequency (more red). Certainly, attaining near-light-speeds is dangerous and difficult. We're not talking "bullet" fast, we are talking "cosmic ray" fast.
However, there is an oh-so-tiny Doppler shift when *any* motion is involved with light. When your friend walks towards you, the light bouncing off of him is slightly more blue. When he walks away, it is slightly more red. Good luck actually detecting this, however.
Photonic crystals have the strange property of behaving like a piece of glass at one moment, and a mirror the next, depending on how much pressure is applied where.
So, using a proper push on the crystal, it is possible to set up a travelling hall of mirrors. The light appears to be slightly shifted due to the Doppler effect to the mirror, so when it is reflected, the light is shifted, by an oh-so-tiny amount. Multiply that shift by a kazillion reflections, which is quite possible if you make the hall of mirrors very tiny (think atomic scale), and you can control light to almost any frequency, high or low, depending on how you set up the mirrors.
So, the net effect is light goes in at one frequency, and comes out the other end at another, without expending hardly any energy to get it done.
The engineering challenge is configuring the crystal so that it can withstand the forces that need to be applied, and applying the forces in a controllable way. Right now they are doing tests with bullets and crystals, because they only need to record data for the instant that the shock waves are travelling through the crystal, and they don't mind using a cheap, destructive method. In the future, they will probably use sound waves to control the crystal. But how they configure this is left to the imagination.
The applications are numerous, and some of them are listed in the article. Needless to say, if we want to use light to transmit data, the more control we have over the light, the more effective we can be in transmitting that data. Also, doctors will be happy because we can now easily exploit the Terahertz range for X-ray type applications.
The radical sect of Islam would either see you dead or "reverted" to Islam.
Thank god... now just before Zephran Cochran launches, we'll have the frequency shifting lasers we need to stop the Borg without any help.
This is certainly an interesting result, but its heavily hyped as well.
First of all, there are many many ways to shift the frequency of light, both up and down in frequency, with both linear and nonlinear means, - from the Raman effect in optical fibers (scattering off vibrations of silica molecules) to Optical Parametric Oscillators (nonlinear wave mixing), supercontinuum generation (using a multitude of nonlinear effects to generate broad bandwidth from a single laser) to simple OEO conversion (detect your light with a photodiode and use it to drive another laser at a different wavelength. Contrary to what this article implies, these effects work at modest power levels in todays optical fibers, and many are highly efficient, and work over extremely broad bandwidths. For example, supercontinuum generation can generate light sources with bandwidth covering the entire visible, UV and IR spectrum in one source! If you want to talk about bulk optic techniques for wavelength conversion, the list is even longer.
Now think a minute about what these guys are proposing. They have to shock the crystal. Initial experiments will destroy the sample. Maybe they can refine the technique down the line to nondestructively shock the sample, maybe they can't. Certainly, infinite bandwidth won't be available, since the amount of wavelength shift will depend on the amount of shock. A single shot technique for wavelength shifting, while interesting, isn't all that useful practically.
Second, they are using a shock, so conversion of CW light is out of the question, only pulses can be converted here, or you risk a time dependent wavelength shift, as your shock dies out.
Finally, claims of a completely new physical effect seem somewhat overblown. It is an interesting idea, but Doppler shifting off acoustic shocks, and photonic crystals are well known. Marrying the two together and finding a stable regime of operation is novel, but not quite the same as discovering a new physical princple like relativity or quantum mechanics, for example.
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The unaltered 'band-gap' crystal structure traps some quantum energy states and lets others pass through. When a shockwave meets the crystal, the traversing wave is momentarily 'held-up' if the shockwave is travelling in the opposite direction or 'hastened' if the shockwave is travelling in the same direction, thereby compressing or stretching the frequency. Since 'band-gap' crystals apply to all waves and not just photonic, this same method can be applied to sound and heat waves as well. Check this excellent Wired article for more. This whole field is really elegant.
RICERCAR
If I make a pun too, do I have to walk the Planck?
The article mentions an interesting fact that the researchers are using bullets instead of sound shock waves. "That will, of course, destroy the crystal"... I can just imagine what goes on in that lab:
"Allrighty, George, it's your turn with the gun."
"But Bill, you know George can't hit the broad side of a barn!"
"Nonsense, my dear fellow. We need to produce some blue light soon, and that calls for a once-in-a-blue-moon event. Come on, George; ready... aim... fire! Take the safety off first, George. Gees... you call yourself a scientist? Ready... aim... fire!"
"Oh, no, not my brand new spectrometer!..."
"Look... Blue light! Woooohoooo!"
Yes, puns are bohring
Seriously, Don't take anything I say seriously.
converters IR->visible are widely known: night vision goggles.
converters UV->visible do also exist and are commercially available, they are not as common because they do not have so many applications (one of them is to detect corona discharge in high voltage applications, power lines). They use a stack of a photocathode (UV light->electrons), Micro Channel Plates (amplification) and a Phosphor Screen (electrons->visible light).
Really? They make me beam
I think that covered the spectrum.
-- To airer is humen
IANAP[hysicist], and so I have some questions about this process.
What I know:
So, when light is converted to a higher frequency (shorter wavelength) where does the necessary energy come from? The shockwave? What about when it is converted to a lower frequency (longer wavelength)? Where does the excess energy go? If the conversion really is 100% efficient (I'm a bit skeptical of that claim), then just imagine the solar panels we could have; sucking up all the UV raining down on us and emitting a soft red glow.
Fascinating stuff. I've got to study more optics and electromagnetic physics.