So yeah, instead of using boring old population-inversion in a gain medium for your lasing fun, with all the attendant waste heat that produces, these blokes have come up with a better way. Two hundred and fifty times better, in fact. And it sounds like Star Trek.
A polariton is a combination of an exciton (which itself is a combination of an electron and the hole that electron would normally otherwise be occupying in a solid state medium) and a photon, which apparently takes a fair bit of precision to pull off. These polaritons then accumulate in a particular energy state before decaying, emitting their photons coherently: laser light. All from gallium arsenide, some clever design, and some electricity, and their design even works at room temperature.
(Actually, is it even appropriate to call the produced beam a laser? Stimulated Emission isn't involved in the process, I don't think?)
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its still a coherent emission of light so i think "laser" can still apply in an informal sense.
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the laser is not exactly high output. it's exciting because it has the potential to be significant, not because it is going to change anything right this moment. if you've ever owned a laser pointer, you've owned a laser that is orders of magnitude more powerful than the one they're talking about in that article.
on a side note, i suspect this system is actually only 250 times as efficient as other polariton lasers, not so much as compared to conventional lasers. why, you ask?
well, the article makes a big deal of the fact that it doesn't require extreme cold temperatures. that's very significant. in fact, that's probably *why* it's so much more efficient. not having to drop temperatures to sub-zero range is very significant, and will undoubtedly save an absolutely absurd amount of energy.
most notably, regular lasers don't require those extreme temperatures to function, either. lasers functioning at room temperature is perfectly normal. your CD/DVD player does not require extreme cooling, nor does a laser pointer, nor do the lasers used for laser tag or really just about any other function.
to me, this suggests that the laser is actually a massive advancement relative to other polariton lasers, not relative to conventional lasers. it may some day become a superior option to a conventional laser. in fact, the scientists involved certainly seem to think it will. but 1/250th is a completely absurd difference in efficiency, and it doesn't fit the facts. that would mean that, at best, a laser would be 0.04% efficient in use of power, assuming this system is 100% efficient (which is so absurdly improbable and far more noteworthy than any silly 1/250th figure). that would mean that a laser capable of outputting a beam which will cut metal is spitting out 250 times the amount of energy required to burn through metal around it, which would have some very unpleasant implications for anyone standing near it, and some particularly unpleasant implications for the laser and housing.
the main thing they talked about is that you can make these things very very small, which will allow for smaller electrical components. that's their big advantage over conventional lasers. not 250 times efficiency values.
Shark_Force wrote:on a side note, i suspect this system is actually only 250 times as efficient as other polariton lasers, not so much as compared to conventional lasers. why, you ask?
This bit from the article seems to imply that this particular design is 250 times more efficient than a conventional GaAs laser:
The article wrote: The new prototype requires 250 times less electricity to operate than its conventional counterpart made of the same material.
I'm pretty certain none of the polariton lasers are considered 'conventional', since they're all pretty much unique experimental designs.
"Then you can simply spead the ground dried corpse bits amongst the plants as needed." - Sir Ysbadden
"There weren't many nukes launched in the apocalypse, so the nuclear winter wasn't that bad." - Killer Cyborg
Shark_Force wrote:on a side note, i suspect this system is actually only 250 times as efficient as other polariton lasers, not so much as compared to conventional lasers. why, you ask?
This bit from the article seems to imply that this particular design is 250 times more efficient than a conventional GaAs laser:
The article wrote: The new prototype requires 250 times less electricity to operate than its conventional counterpart made of the same material.
I'm pretty certain none of the polariton lasers are considered 'conventional', since they're all pretty much unique experimental designs.
and yet the sentence before clearly states that they're predicting it to be more efficient than traditional lasers. you don't need to predict squat if you have experimental proof, particularly if it's by that large of a margin.
far more of the article is spent discussing the differences compared to other polariton lasers.
and, as i said, the only plausible way i can imagine needing 1/250th of the energy is if it's the difference between needing extreme cold temperatures, and not needing it.
seriously, unless they either suck so bad at math that they can't figure out that 250 times more efficient requires a conventional laser to be 0.04% efficient (anything more than that would mean that their laser is actually more than 100% efficient, which would be significant enough that the whole world would be hearing about it because it would actually be both a laser and a power generator. or, more likely, would mean that they don't have the slightest clue how to do science), that much of an increase in efficiency requires such ludicrous inefficiency in traditional lasers as to be unbelievable.
Shark_Force wrote:and yet the sentence before clearly states that they're predicting it to be more efficient than traditional lasers. you don't need to predict squat if you have experimental proof, particularly if it's by that large of a margin.
far more of the article is spent discussing the differences compared to other polariton lasers.
and, as i said, the only plausible way i can imagine needing 1/250th of the energy is if it's the difference between needing extreme cold temperatures, and not needing it.
One of the reasons it's so much more efficient is because it doesn't rely on having to establish and maintain a population inversion in a lasing medium. This is where the bulk of the energy a laser consumes ends up.
seriously, unless they either suck so bad at math that they can't figure out that 250 times more efficient requires a conventional laser to be 0.04% efficient (anything more than that would mean that their laser is actually more than 100% efficient, which would be significant enough that the whole world would be hearing about it because it would actually be both a laser and a power generator. or, more likely, would mean that they don't have the slightest clue how to do science), that much of an increase in efficiency requires such ludicrous inefficiency in traditional lasers as to be unbelievable.
You can't have greater than 100% efficiency. Thermodynamics gets mad at you when you do that.
Conventional lasers aren't terribly efficient (somewhere around 10-15% IIRC). But what they're saying is that for the same output, the polariton 'laser' uses 250x less power. It still has to follow the rules.
"Then you can simply spead the ground dried corpse bits amongst the plants as needed." - Sir Ysbadden
"There weren't many nukes launched in the apocalypse, so the nuclear winter wasn't that bad." - Killer Cyborg
if a laser uses X amount of energy to generate Y amount of energy output, the efficiency is Y/X, is it not?
then if a polariton laser uses X/250 to generate Y output, the efficiency of the polariton laser would be Y/(X/250)
so let's suppose, to get your 10-15% range, we go with values of 100 for X, and 10 for Y.
that gives us 10% efficiency for the conventional laser.
then we go to the polariton laser. that would be 10/(100/250), which is 10/(0.4), or 2500%
which, as you noted, doesn't play nice with our current understanding of physics, and would certainly be far more significant than any blather about producing coherent light.
if they're getting 250 times efficiency, then someone is leaving something out of the equation somewhere.
Shark_Force wrote:if a laser uses X amount of energy to generate Y amount of energy output, the efficiency is Y/X, is it not?
then if a polariton laser uses X/250 to generate Y output, the efficiency of the polariton laser would be Y/(X/250)
so let's suppose, to get your 10-15% range, we go with values of 100 for X, and 10 for Y.
that gives us 10% efficiency for the conventional laser.
then we go to the polariton laser. that would be 10/(100/250), which is 10/(0.4), or 2500%
which, as you noted, doesn't play nice with our current understanding of physics, and would certainly be far more significant than any blather about producing coherent light.
if they're getting 250 times efficiency, then someone is leaving something out of the equation somewhere.
I imagine it would be more sensible to calculate it in terms of waste energy, eg. a laser that is 10% efficient is wasting 90% of its energy. This device would waste 250 times less, so you'd end up with something around 99% efficient (100%-90%/250). Though honestly I have no idea how they're actually calculating it.
Edit: It's entirely possible that number is also the result of science "journalism", if you know what I mean.
"Then you can simply spead the ground dried corpse bits amongst the plants as needed." - Sir Ysbadden
"There weren't many nukes launched in the apocalypse, so the nuclear winter wasn't that bad." - Killer Cyborg
the kind of things that get over 90% efficiency are devices which are designed to generate heat (thus making what would normally be wasted electricity released in the form of heat actually become useful), and transformers (which don't actually have a load, and thus are basically only dealing with the resistance of the wire).
but that isn't what they said. they specifically said it uses 250 times less electricity, not that 250 times less is wasted.
also, even if the 250 times less figure was something the journalist reported to make it sound more impressive, i rather doubt said journalist came up with that number out of nowhere. it's probably based off of something that someone told the journalist.
i'll grant that the journalist may have taken something out of context, but that still requires that someone, at some point, told the journalist that something was 250 times as efficient in this thing.
also, if we're going with the assumption that the journalist is overstating the increase in efficiency, we're right back to saying that there's no way this thing is 250 times as efficient as a conventional laser. it may be more efficient. but 250 times as efficient? that's crazy.
Shark_Force wrote:99% efficient is also ludicrous.
the kind of things that get over 90% efficiency are devices which are designed to generate heat (thus making what would normally be wasted electricity released in the form of heat actually become useful), and transformers (which don't actually have a load, and thus are basically only dealing with the resistance of the wire).
but that isn't what they said. they specifically said it uses 250 times less electricity, not that 250 times less is wasted.
also, even if the 250 times less figure was something the journalist reported to make it sound more impressive, i rather doubt said journalist came up with that number out of nowhere. it's probably based off of something that someone told the journalist.
i'll grant that the journalist may have taken something out of context, but that still requires that someone, at some point, told the journalist that something was 250 times as efficient in this thing.
also, if we're going with the assumption that the journalist is overstating the increase in efficiency, we're right back to saying that there's no way this thing is 250 times as efficient as a conventional laser. it may be more efficient. but 250 times as efficient? that's crazy.
I guess I'll have to wait until the actual paper gets released before I can figure out what they actually mean by it / where the journalist went wrong.
Edit: I think I might have an idea what they're on about. The "250x less power" statement is referring to the fact that polariton lasers have almost no lasing threshold; you need to pump lots of power into the medium initially to get a regular laser to start up, where a polariton laser will start emitting coherently more or less immediately. So I guess it is one of those "science journalism" moments: sort-of correct, and yet completely misleading.
Still, it's a pretty awesome discovery. And it has a great name.
"Then you can simply spead the ground dried corpse bits amongst the plants as needed." - Sir Ysbadden
"There weren't many nukes launched in the apocalypse, so the nuclear winter wasn't that bad." - Killer Cyborg
1) This is not a scientific publication, it is a journalist writing an article about something they don't really understand.
2) They have been working on this for years, and there have been a number of papers on the idea and on this specific work at this specific lab. "Solid State Electrically Injected Exciton-Polariton Laser" was published in Physical Review Letters 110 last year.
3) The efficiency thing is something that got badly distorted for the article. It is comparing to one very particularly inefficient kind of laser, and it is comparing only the start-up energy. Most lasers are not cooled to below zero, if anything they are simply cooled to keep from melting - they still run hot! The big thing it a laser cavity is typically holding onto hundreds of times the energy it is emitting in any given second, because that energy is needed to sustain the process.
4) TAANSTAAFL - Once that start-up energy has been invested. wall-plug efficiencies can be down in the 1% range or higher than 30%, and you cannot, cannot by 250x more efficient than that without breaking the laws of physics... which they have NOT done.
