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GreenD
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Change wavelength of light?
I'm not very knowledgeable in quantum mechanics but this has been a holy grail for me:
Can we change the wavelength of light (a photon)?
I.E. could we have a green laser in which the emitted light goes through some apparatus, and the product being blue or red shifted?
The end application in my eyes would be ultra-efficient solar cells. They have succesfully "reverse" engineered a laser to convert >95% light
energy of a secondary laser to electrical potential.
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Neil
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Grab a laser, turn it on and tape it to your head pointing forwards or backwards then run away. You have changed the wave legnth.
Besides playing with acceleration, as far as I know there are no really simple effective ways of changing the wave legnth. dichromatics will let you
split off any frequency you wish and you can use that to fire parts of a white beam onto what ever membrane will absorb them best but afak you can't
shift the frequency.
My understanding is that currently they stack multiple layers of photovoltaic material so that each layer gets a certain wave legnth.
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neptunium
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its possible to go down the scale of frequency but i am not sure its possible to go up.
in a neon sign UV light is absorbed by the phosphor and re emited in the visible spectrum (most of it)
the doppler effect previously mentionned works great ...at speed comparable to the speed of light!
gamma rays can be absorbed and re-emitted in lower wavelenght as well but if i understand your question is can you also do it the other way and that
would involve an external energy kick of sorts, or something else got to give when doubling freqencies.... the extra energy has to come from somewhere
[Edited on 30-1-2012 by neptunium]
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Polverone
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Most green laser pointers work by frequency doubling a 1064 nm infrared beam to a 532 nm green beam. I don't know if the trick can be pulled off with
non-coherent light sources.
PGP Key and corresponding e-mail address
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Morgan
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I found this tidbit, I don't really know much about lasers. I remember in high school seeing an invisible beam of light going through a crystal
popping out green in a Science and Technology encyclopedia, in the days when I was interested in growing crystals.
"Finally... MOST green laser pointers are not really green - they are using an IR laser and then using a frequency shifting crystal to achieve green
(makes the cost of the laser less expensive)."
"Do NOT take apart such a laser. If you remove the crystal you now have an IR laser that is probably 2 to 5 watts (for a 150 mw green pointer) - this
is EXTREMELY dangerous and invisible."
"I have lasers throughout my house - up to 500 mw. I have Class 3B and 4 Lasers - and all my exterior doors have outside signs that read "hazardous
lasers in use - eye protection required at all times"."
http://www.reddit.com/r/askscience/comments/l1y1a/does_the_c...
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aaparatuss
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Wikipedia isn't exactly like some illuminating resource
but research into the Compton effect is the exchange of energy between photons and matter...
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Twospoons
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Quote: Originally posted by Polverone  | | Most green laser pointers work by frequency doubling a 1064 nm infrared beam to a 532 nm green beam. I don't know if the trick can be pulled off with
non-coherent light sources. |
Yes it can, but not in the same way. The green laser uses a non-linear optic (a KTP crstal) to create the second harmonic of 1064nm. this requires a
high optical flux to bias the material into the non-linear region.
The second method uses fluorescent materials that can be illuminated with IR and emit in the visible range. Efficiency is poor, from memory. They work
by absorbing two photons to energise an electron, which then jumps back to ground state and emits a single photon of a shorter wavelength. Search for
"IR finder card" for an application - locating IR beams in optical bench setups.
[Edited on 31-1-2012 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
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Pulverulescent
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| Quote: | | Grab a laser, turn it on and tape it to your head pointing forwards or backwards then run away. You have changed the wave legnth.
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I hate you! I hate you! I hate you!!!
You've gone and ruined it for me!!!
I was supposed to say; tape it to a fast rocket pointing backwards and fire the rocket!
Or jump on a train and look back at it. ( )
P
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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AndersHoveland
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Yes, it is not impossible to, for example, convert red light to blue light.
I have a book about non-linear optics. Addition, subtraction, and doubling of frequencies is possible.
What you have to remember is that photons are absorbed and reradiated by their transmission medium. Usually the photons will tend to progress without
alteration, or with only deflected paths but no change in frequency (linear optics). This is due to the phenomena of coherence, where the effected
dipoles simultaneously reradiate in unison. But under certain conditions it becomes more favorable for other interactions. One of the simplest of
these setups is a beam refractive beam splitter, where two lasers of different frequencies can merge into one beam which will have a fequency that is
the sum of the frequencies of the original beam. The angles of the incoming beams must be carefully matched to the refractive index of the beam
splitter. The first pass efficiency of such a setup is very low, less than 1 percent. Actual non-linear devices rely on much more complicated setups,
and the optics must meet exacting engineering standards. Attempting to make a non-linear device would be nearly impossible for the amateur. There is
also much to consider because in practice the refractive index shows some variability over the wider frequency ranges at which such devices operate.
The highest conversion efficiency for a non-linear optical device is the same that is used in green lasers, and is about 25 percent.
No, it cannot as much as I understand from the book. To obtain any significant conversion in the frequency of light from non-linear optics, the
frequency and direction of the beginning light must be specifically selected. There is, however, much theoretical potential for photonic crystals,
which would mostly reradiate light in a specific frequency.
The phenomena of non-linear optics should not be confused with fluorescence. Simply passing an ultraviolet laser (N2) through a solution of
fluorescent dye can convert some of the uv beam into a vissible laser beam.
N2 lasers are surprisingly easy to make, just an air gap is needed (no glass container or mirrors!).
http://photonics.tfp.uni-karlsruhe.de/1/a-homemade-uv-laser....
http://www.youtube.com/watch?v=svSUzUBSkD4&feature=relat...
[Edited on 31-1-2012 by AndersHoveland]
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GreenD
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Ok - obviously understood that phosphorescence and fluorescence produce the desired effect. Perhaps I should give this more thought, anyways.
My adolescent knowledge in the field of optics and photonics tell me that energizing a source (probably a metal or crystal) -[how, I don't know] -
could add the energy to the photon. But that is the question, how do you add that information.
Anders- I am really not qualified for this discussion, I'm finding. I do not know the difference between non-linear optics and linear. I thought all
light was linear, with the exception of (strong) gravity and relativistic speeds. You brought up the idea of combining two lasers of different
frequences merginig into one beam in which the frequencies are the sum - This is true? This is basically what I am looking for. I'm not planning on
building my own but could you possibly explain this concept? Why does this not happen with ... any crystal (i.e. if it did, all light in a crystal
would be blue shifted to some degree).
I'd like to know more about this!
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AndersHoveland
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| Quote: Originally posted by GreenD |
I am really not qualified for this discussion, I'm finding. I do not know the difference between non-linear optics and linear.
|
"Linear" optics is just "normal" optics, where it is simply the direction of the light that is changed. "Non-linear" optics manipulates other
properties of the photon, usually frequency. But actually a photon has many different properties that are not often thought of, for example
polarization (a photon can also be circularly or elliptically polarized!) and angular momentum (basically the photons can all be spinning in one
direction, and this energy comes in quantum units called hbar). So it is not theoretically impossible to make a laser beam that could cause the target
to physically rotate.
| Quote: Originally posted by GreenD |
My adolescent knowledge in the field of optics and photonics tell me that energizing a source (probably a metal or crystal) -[how, I don't know] -
could add the energy to the photon. But that is the question, how do you add that information.
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If you try to "energise" the crystal, it will tend to just immediately give up its energy.
I will try to explain this as simply as possible. If two different frequencies of light are travelling together along the same path, same direction,
in a crystral, some (a very small fraction of 1 percent) of the photons of different frequencies will add together. But the type of crystal must be
carefully selected, because it must be transparent to all the frequencies. Glass is actually only transparent within a relatively narrow window of
frequencies, the vissible range. Typically fluoride glasses are used.
In practical frequency doubling devices, mirrors are used to bounce back and forth the beginning frequencies of light, because the first-pass
conversion rates are so low. The light must pass through several times before any significant fraction of it is converted.
I wish there was an easy educational site to explain this phenomena to you, but unfortunately there does not seem to be.
The actual concept is very simple, but in practice the construction of the actual devices themselves are very complex.
If a part of a crystal simply has two different laser beams passing through it, there will not be any significant frequency doubling. Although the
crystal is "energised" (for lack of a better word), conditions are not optimal for that energy to be radiated out as a new frequency. Usually the
phenomena of coherence or interference is used to "reinforce" or "supress" the desired or undesired frequency. In other words, the device is built
such that if the crystal just behaves how it normally behaves, there will be much destructive interference. So the probabilities are shifted. This
setup typically involves a resonance cavity not unlike a normal laser.
| Quote: Originally posted by GreenD |
You brought up the idea of combining two lasers of different frequences merginig into one beam in which the frequencies are the sum - This is true?
This is basically what I am looking for. I'm not planning on building my own but could you possibly explain this concept? Why does this not happen
with any crystal?
I'd like to know more about this!
|
In the attached picture is a diagram of the simplest possible frequency summing arrangement. This is not the exact configuration that is practically
used, but it is illustrative of the basic concept.
Potentially any type of crystal could work, but in actual practice the crystal needs to adhere to exacting specifications. Some types of frequency
summing devices also use bifringent crystals.
In the diagram, you will notice the reflectors. There is not going to be any significant conversion unless to the light is passed back and forth many
times. This is not only important for the original frequencies, but also for the resultant frequency so it can "amplify" (constructively reinforce)
itself. The two reflectors act as a resonance cavity.
[Edited on 2-2-2012 by AndersHoveland]
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ThatchemistKid
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Maybe this will give you a couple of ideas, I do not know much about this so here is my 2 cents
http://en.wikipedia.org/wiki/Raman_scattering
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GreenD
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Anders that all makes sense, it seems elemental, although I'm sure the actual mathematical and quantum understanding is a bit more complicated. I,
also, wish there were a simple tutorial on this.
I'll have to look up raman scattering later.
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AndersHoveland
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Here is another good amateur site:
http://www.milankarakas.org/pub/KDP/HomegrownKDP.html
Also for a nitrogen laser:
http://www.milankarakas.org/pub/New_TEA_N2_1/TEA_N2_1.html
(note this laser does not have any mirrors or gas containment)
Also, a correction, made a mistake in that picture; the output will have a higher frequency so it will not be refracted as much, so the purple beam in
the right diagram should be on the other side. 
[Edited on 14-2-2012 by AndersHoveland]
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White Yeti
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This may or may not be what you are looking for, but what if you split sunlight into all its wavelengths with a prism. Then, you can block out all the
wavelengths that you don't need, and there you have it, a tuneable light source.
As for "changing the wavelength of a photon", things get tricky. A photon is a package of energy, the only way to change its wavelength (and energy)
is to let it strike a material that will absorb it and emit another photon of a lower energy. This is not predictable, as there are many ways an
electron can fall back to ground state.
However, you can tune an electromagnetic wave. If you find a way to control the oscillations of electrons in a Free Electron Laser, you can tune the
frequency and thus the wavelength of the beam of light.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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AndersHoveland
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| Quote: Originally posted by White Yeti |
A photon is a package of energy, the only way to change its wavelength (and energy) is to let it strike a material that will absorb it and emit
another photon of a lower energy. This is not predictable, as there are many ways an electron can fall back to ground state.
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Coherent photons are transiently absorbed into transparent dielectric mediums, and can be reemitted as in multiples, sums or differences (if two
different initial frequencies are used) if the desired frequency is amplified/reinforced by an appropriate resonant cavity that favors the desired
frequency.
Also, photonic crystals can convert lower frequencies into a specific higher frequency. But technical problems have so far prevented photonic crystals
from converting frequencies in the vissible range.
[Edited on 18-2-2012 by AndersHoveland]
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Mr. Wizard
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Common 'White" LEDs contain a phosphor ( Stokes Shift) in front of the blue LED inside them that reemits yellow light. The combination of the blue
and yellow light is interpreted by our eyes as white.
Details can be found in the white LED section of :
http://en.wikipedia.org/wiki/Light-emitting_diode
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daragh8008
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One way to convert the wavelength of light is by deep level defects in semiconductors. An example of which would be copper doped ZnO. The band gap of
zno in the uv region so it absorbs light very well just outside the visible region ( 380nm iirc) the copper dopant emits a broad green band. I'm sure
there are other semiconductors that could be also used for this process and who's defect emissions coul be tailored for the application. Although I
would imagine that the process is not particularly efficient. Moving from long wave lengths to short is not as easy. As mentioned above second
harmonic generation is one way as is multi photon absorption processes but all very inefficient. Since the end application if solar cells I think the
best line of attack is photon trapping / total internal reflection thin film cells rather than wavelength shifting. But that's just my opinion.
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peach
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| Quote: | | Can we change the wavelength of light (a photon)? |
Certainly.
Phosphors / Fluorescent dyes (e.g. Fluorescent light bulbs / tunable dye lasers):
If you go to the whimsy section and look for my post 'The secret life of...' and then click the light bulb episode, you'll see the presenter
demonstrating the effect these coatings have on the bulbs spectrum. They are absolutely key to the bulb manufacturers, are patented, and have been the
cause of arguments; e.g. Osram receiving large grants from the German government as 100W incandescent bulbs were forced into phase out.
<img src="http://img.directindustry.com/images_di/photo-g/tunable-dye-laser-84815.jpg" width="800" />
Frequency multiplying crystals (the lower image is of one of the KDP crystals grown for the National Ignition
Facility):
Quantum Wells / Dots:
<iframe sandbox width="640" height="480" src="http://www.youtube.com/embed/MLJJkztIWfg" frameborder="0" allowfullscreen></iframe>
---------------------------------------
The problem is not it being physically impossible, it's the practicality.
The dyes and quantum dots can fade when exposed for prolonged periods.
The crystals can be hydroscopic and will dissolve if exposed to the elements. A number of the materials used can not be wet machined, honed or lapped.
Instead, they are cut using very high precision lathes. The lathes use a single diamond point and can achieve surface finishes in the nanometer (near
atomic) range, with only air blowing over the tool. Such technology is not standard by any means, Moore Nanotech make a few tens of these lathes per
year.
<iframe sandbox width="640" height="360" src="http://www.youtube.com/embed/vAvfrrlMZg4" frameborder="0" allowfullscreen></iframe>
Many of the people looking into viable solar farms do not use traditional solar panels, but Stirling engines. The Stirling engine is the oldest and
simplest form of engine. They can be incredibly reliable and efficient. Rather than growing expensive wafers and special coatings in silicon plants
(an inherently expensive source of material), they use a black body absorber and the heat to drive the engine (which can be made on traditional
machinery).
The design can be very simple; a big sheet of metal bent into a curve with a pipe at the focal point.
Brian Cox gave some good examples in his program on nuclear fusion; How to build a star. People in the UK use around 10kWh of electricity per day.
Assuming we wished to provide 5kWh to everyone in the world over the next few decades, that would mean building two or three fission plants per week
(or was that per day?). And the numbers of panels / turbines is staggering. Not accounting for population growth.
New Scientist was all about fission this month. Of the 170 odd fission plants officially shutdown, only 17 have been fully dismantled since the start
of the nuclear era. As a result of the Fukushima accident, Germany won't be building anymore and will be shutting it's down. Japan may follow suit.
That alone will produce around another 320 million tons of CO2 by 2020 (2025?), which happens to be the same amount that was intended to be saved by
European carbon cuts; nulling them out.
They would all help, along with better insulation in homes, but fusion is the only real solution to the problem. Particularly if we intend to move
forward. It's important we don't waste money that could have been spent on fusion on things that won't do a whole lot.
The UK has the most successful nuclear fusion for power program, and we spent more on ring tones last year than we did the program. Korea is a late
entry, with the final experimental prototype to come online and polish up the design.
K-Star light up in 2008 and is managing 20 seconds of burn time at present, upgrading to 300 soon.
All the work will be rolled out as the prototype power plant ITER (International Thermonuclear Experimental Reactor). Construction has already started
in the South of France.
Edit: I thought you might also be amused to know that such light manipulating technology is all around you. Many of the 'whiter than white' detergents
for shirts contain UV dyes that cause them to literally glow blue during the day. The blue helps 'whiten' the red, orange and yellow in the light they
reflect. You can see the effect very clearly in night clubs that have a black light. The same is also applied to bright white paper, which glows blue
when hit by a UV laser.
Many, many, many molecules can shift frequencies of light and can be seen glowing on TLC plates under UV lights or in the detectors of (U)HPLC.
This girls outfit and make up are absorbing deep blue / long UV and re-emitting it at lower frequencies.
Below is an image of a Claviceps paspali (ergot) culture. The final photograph showing the culture glowing green under UV due to the presence of the
lysergides.
[Edited on 20-3-2012 by peach]
<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced
image size(s)]
[Edited on 7/25/13 by bfesser]
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497
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Wouldn't it just be easier to invest in ways to use less electricity? How much of that 10kwh per person is really necessary? Many of our current
systems were designed with efficiency as a low priority. People with off grid houses commonly get down to 2-4 kwh/day per capita using outdated
technology. If a concerted effort was made to develop better appliances and systems, it could be improved even further. And really, I think
nonwesterners could happily use less because they won't see it as a reduction in standard of living.
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peach
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That is true, to an extent.
Many of the electrical appliances in your house have already been highly optimised. People who manufacture semiconductors are
hardcore on efficiency (harder than anyone else I expect), because the main problem they face is heat build up; they spend more than
a few lottery wins just on heat. Similarly, switch mode power supplies are present in many appliances to drastically reduce losses. And light bulbs
are now ten times more efficient than incandescents.
A light bulb might waste 10... 50W, whereas my boiler is around 30,000W. The issue is heat loss (in the UK). In the US, it's often heat gain (having
to run air conditioners all day).
Have a watch of these videos from Matt in this post about Net-Zero buildings.
I have hugged a tree, and love nature. But many of the green power people and off griders have highly suspect ideas of how the world works and an
unrealistic method of living. They have that technology because someone else has paid the bill for them, in developing the technology. There is not a
chance we would have things like Hubble, or solar panels, or even loom made cloth, had the hippies of society gotten everything they wanted.
During the industrial revolution, England was smogged out with coal soot. We needed that to develop far cleaner burning and higher efficiency tools
and ideas. And from it we have gained many incredible things; medicines, semiconductors. The petrochemical age we live in now is the same. It is a
problem but, provided it's focused correctly, we will move on; this time, for a change, to something that is genuinely far more powerful and
exceptionally clean.
I have spent much time looking into this and, even as a tree hugger, I would prefer we burnt the stuff and got fusion going. Anything less and we'll
halt or move backwards.
Hard green advocates are rabbits in headlights.
[Edited on 20-3-2012 by peach]
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White Yeti
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How about using solar energy to drive processes that require large amounts of process heat? What we are doing now is converting coal into electricity
and electricity back into heat. From an economic standpoint this is the way to go because we have huge reserves of fossil fuels and it's easier to
transport electricity. From a thermodynamic standpoint, this makes no sense at all.
We have to find a better way to store and use heat.
70% of the electricity we produce is turned back into heat in chemical plants and factories for heating stuff up.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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peach
Bon Vivant
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That's also true.
Part of an off-gridder scheme I do think is good is home generators. These take the gas or oil, burn it, produce electricity and then use the heat in
the exhaust to warm the house, so it all gets used. Micro machining is also trying to produce minute heat recovery engines and generators for more
portable appliances. If this could be rolled out in semiconductor plants, which can produce millions of units for not much, it would be great. As it
stands, things like thermocouple piles are terrible. They're only used on satellites going into interstellar space due to the necessity.
Electricity is simply far easier to transmit, with far fewer losses, than heat; here on earth. Moving the factories and plants closer to (into) the
generation site would require a monumental (unified world) effort, and we'd still be dumping CO2, from a finite resource.
Fusion. It's the hippy's dream. They just didn't (don't) realise it.
[Edited on 20-3-2012 by peach]
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GreenD
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I agree fusion would be incredible. It is nearly free energy... I don't know the exact physics (what fuel sources they use) but it seems to me like
the holy grail of the human race. If we advance fusion, there all energy sources should be secured.
However, I'm always curious what a fusion melt down would be like?
Caltech and the 80-96% efficient solar cell: http://media.caltech.edu/press_releases/13325
Don't know why this hasn't been plastered on the front page of everything.
On topic - peach I was aware of fluorescence and phosphorescence, and perhaps they are just what I was looking for. I haven't given this much thought
in a while and need to go back to the drawing board.
ʃ Ψ*Ψ
Keepin' it real.
Check out my new collaborated site: MNMLimpact.com
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peach
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The fuel is deuterium-tritium. It comes from seawater and lithium. We have an enormous amount of sea water and lithium is one of the most common
elements.
It's product is helium, a rare element needed for high end science.
It is entirely impossible for a melt down to occur in a fusion reactor.
For fusion to occur, on earth, the temperature has to be in the hundreds of millions of degrees Celsius.
There is absolutely no material on earth that can withstand that without boiling; it all turns into plasma at those temperatures (which are ten times
higher than the core of the Sun). The state change absorbs huge amounts of energy; cooling and quenching the reaction.
The key to the hippy nature of fusion is that a fusion reactor does not require a pile.
The key the downfall of fission is that it requires a pile.
A fission reactor is like filling your house with propane and then trying to light a corner of the room to stay warm, but not incinerate the house.
Hard. When it goes wrong, the whole thing goes up.
A fusion reactor, like a normal fire, is fed the fuel as it needs it. There is no way the fuel could flashback and burn, because it's about a hundred
million degrees too cold to do so. The evidence is given by how hard it is to get the thing to work in the first place. The experimental reactors can
achieve those temperatures, but it is hard to maintain them even when surrounded by teams of leading experts and superconductors.
The problem is not insulation, it's turbulence. The plasma is moving at an appreciable fraction of the speed of light. Any minute disturbances in the
magnetic bottle of the toroid cause it to go into oscillation, which eventually crashes it through the field and into the walls.
If a fusion reactor went awol, it would simply vaporise a few mm of it's reactor's lining and that'd be it. There is no pile. This is a common
occurrence for the prototypes.
There is also no weapons grade material coming into or out of the plant. Massively reducing the risk when selling it to other countries or
transporting the materials.
It would require around a bath tub of sea water and a laptop battery's worth of lithium to power a house for an entire year.
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