Graphene Yields Another Trick: Ultrashort Laser Pulses 24
ananyo writes with this excerpt from Nature News: "Experiments suggest that [graphene] can be used to create ultrashort laser pulses of any colour, owing to an ability to absorb light over a broad range of wavelengths. So far, the researchers have coaxed the material to produce pulses of radiation from a broad spectrum of infrared wavelengths, which are useful in applications such as fibre optic communications. Their results, together with the known properties of graphene, suggest that the material should be able to yield similar ultrashort pulses over the entire spectrum of visible light as well. The discovery could help researchers to build small, cheap and highly versatile ultrashort-pulse lasers, with potential applications ranging from micro-machinery to medicine."
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Pew! pew!
Obviously (Score:1)
That's Laser in finger quotes :)
Bwahhh Bwahhhh Bwahhhhh
Re:femtosec is not ultra short (Score:5, Interesting)
I just went on a mini wiki binge based on that refutation. Thanks.
It would seem that although femtosecond pulses are not on the scale of the state of the art (attoseconds) they are still considered "ultra-short" by the optics community. The real news would seem to be the range of frequencies that can be produced (both the breadth of frequencies and, specifically, some frequencies that are difficult to work with) and little more.
Only one paper wasn't behind a paywall, and I'm not a trained scientist, (So if I make a mistake someone PLEASE CORRECT ME) but from what I can glean graphene will happily absorb nearly any wavelength of light because of the lack of a bandgap between free electrons and bound electrons (this is the opposite of what you find in, e.g. semiconductors where there is a meaningful power gap). Electrons in graphene can be exited to any quantum level within a wide and useful range. In fact it seems that it absorbs so much of the energy that they had to dope the graphene to reduce its absorption. It is also notable that the graphene wasn't hard to produce. They produced flakes between one and three layers in solution, filtered out the water, cooked for a bit, and the resultant jumble of flakes was A-OK and only ~1/3 graphene by volume. Far easier than producing something more pure or large scale.
The graphene is pumped in a "lossy" mode to bump electrons up in energy (this is the "low Q" or "low quality" resonator mode) and then the resonant cavity is bumped to "high Q" mode. Since the graphene absorbed so much of the pumping light, and did so over the entire bandwidth of the pumping laser, when the mode is switched it lases brightly and all at once. (This is, in short, "how to build a Q-swtiched laser")
The key difference with graphene is that it absorbs practically any frequency of light without any modification. This is the special property, the lack of tuning required for a "saturable absorber". As far as I can tell this means that the material can store a certain amount of energy from the laser pump with low losses until it becomes saturated. I interpret this as a sort of optical capacitor (low loss energy storage) where as more traditional absorbers are leaky capacitors at frequencies that they are not tuned for.
Not sure how significant the optics community will find this, but it does seem to be a meaningful technology rather than a "trick" or some "in 5 years" promise.
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Yay, carbon! (Score:2)
Oh, that graphene. What can't it do?
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Be produced in useful scales?
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Wait a sec... (Score:1)
Does this mean I'll be able to torture cats with a BLUE laser?
Because that's a lot cooler then any of the petty stuff mentioned in the article.
SMAC/X Tech Development (Score:2)
Gatling Lasers? Just need plasma armor and I'm set!
Nature has limited credibiilty (Score:3)
Nature used to be a prestigious, tightly edited scientific journal. Now, it's like the Weekly World News of science. Especially in computing and materials science.
This isn't an article published in Nature. It's a blurb for an reference in Applied Physics Letters to an announcement that's scheduled to be made at the Lasers and Electro-Optics Conference next month. Then we'll find out if this really works. Maybe.
You can't store much energy in a single sheet of atoms. This may generate very weak femtosecond pulses. There are lots of interesting uses for very short laser pulses in imaging. A nanosecond pulse is a foot long.
How short before you aren't a laser? (Score:2)
Is a single photon considered an "uber-short beyond all uber-shortness" laser pulse?
If not, what about to arbitrary successive photons in a laser beam - if all of the photons before and after them were diverted, would these two photons together constitute an extremely short laser pulse?
If the answer to either is yes, how many "laser beam photons" in a row do you need (assuming a single-photon-wide beam) before whether the beam is a "laser" or not has any practical significance? Or is a single-photon-wide l
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How many grains of sand does it take to make a piles of sand?
It mostly comes down to how many you need to do something practical. There are uses for single photon sources and they are used a lot in quantum mechanics research. But you can't really call it a laser, because it is neither coherent or incoherent if you only have one.
In the real world, many times it isn't black and white as coherent and incoherent, either. Sometimes it has to be just coherent enough, and there is a matter over what time an
Woah, graphene again (Score:2)
Is there anything it can't do?