Slashdot Mirror
Quantum-Cascade Polychromatic Lasers
eznihm writes: "This article describes a new laser, developed by Lucent and others, that emits a band of light and operates at room temperature. "The result: a beam of high intensity at every wavelength from 6 to 8 micrometers, in the so-called midinfrared range.""
- monochromatic
- coherent
- low-divergence/parallel
- high intensity
The devices build in this article don't have the first two properties, at least. Indeed the device sounds more akin to a "white" light LED (white in the sense of broad spectrum, I know they are infrared).Of course, these are just properties, and might not actually be a working definition of a laser - maybe if you satisfy the acronym, you're a LASER (light amplification by stimulated emission of radiation, for those that don't know).
I could reach behind me to look at Svelto's "Laser Physics" book, but I'm too lazy.
XML causes global warming.
Quantum-Cascade Polychromatic Lasers!
Quantum-Cascade Polychromatic Lasers!
Quantum-Cascade Polychromatic Lasers!
Quantum-Cascade Polychromatic Lasers!
(I took one look at that and thought Zippy. Oh boy. Excuse me while I fix a peanut butter and olive sandwich...)
--
# Canmephians for a better Linux Kernel
$Stalag99{"URL"}="http://stalag99.net";
And when you weren't burning hair off your body, you could use it to super heat your evil Science Teacher's house so that popcorn exploded out of it everywhere...and you wouldn't even need to hijack the computers on a nearby B-1 bomber!!
Finally, my life can emulate Real Genius!! (thanks Cliff!)
Bell Labs has a page up on a Quantum Cascade Laser at http://www.bell-labs.com/org/physicalsciences/psr/ qc/ with info about its design, applications, and other related info from a few years ago.
Technically speaking this isn't quite true - it depends on what your lasing medium consists of. While each colour line emitted will be monochromatic, a single laser is capable of producing multiple lines.
In the case of a Krypton or Helium Neon ion gas laser you will get a single line out (usually, but not necessarily, red for either of these).
However, if I look at an Argon laser with apropriate optics you get primarily Blue and Green (514nm "Green" and 488nm "Blue") lines (with combinations in between). If I put a prism to the output of my little American Laser 60x I can see 7 individual lines - 5 are of such lower power as to be virtually useless, but the primary Green and Blue are strong.
Then if you look at a Copper Vapor laser which works by evaporating copper you get two lines: an emerald green and *gold* (this type of laser was made famous during the Pink Floyd Division Bell tour).
Newer solid state are very much single line. If you ever see a very harsh green beam you are probably looking at a Nd:YAG laser. The new solid state stuff is really looking promising... much more reliable with a much longer lifespan. Now, if they could just get the Blue solid states more powerful reliable we would be laughing. A low to mid powered white-light lasershow that could fit in a briefcase! On the down side though, typically much lower power output than their ion cousins (and the YAG green is, in my opinion, really nasty).
Could almost make me miss lugging 909's around... :)
"They do not preach that their god will rouse them, a little before the Nuts work loose." Kipling, 'The Sons of Martha'
Typically, you're correct. Traditional lasers emit almost all their energy at a single wavelength, with very small deviations of energy (determined by the time it takes an atom to emit a photon, thanks to the good ol' uncertainty principle, dE*dt>h/(2pi)). What Lucent did here is to create a whole mess of lasers in one package, which all emit slightly different wavelengths. The wavelength uncertainties overlap enough that you get a fairly smooth distribution of energy, rather than a single, well-defined peak at one wavelength.
Bugrit! Millenium hand and shrimp!
ation:)
In answer to all those going, "huh? i thought the whole point of lasers was that they're coherent/all the same wavelength"
Any device which excites one or more substances electrons to jump up an energy level and then fall back generating a specific wavelength (per substance) photon. these are usually bounced back and forth in a chamber and released at one end.
This article is about a quantum cascade laser, which is a bit more complicated than my simplified (even for normal lasers) explaination.
The point is, that while coherent lasers are the norm and coherence has many uses, this is still a laser and the technology may have many different uses itself.
Monocromacity is not an inherent property of lasers.
It's a limitation we could not overcome until now.
Lasers are coherent.
Lucent has created a multichromatic coherent laser.
Simply put, multiple quantum wells laze at different frequencies. Stacks of these multiple quantum wells create multiple lasers in one cavity, if I understand it correctly.
Each frequency is indeed coherent. You get multiple frequencies, however, in one resonant cavity. I'm guessing here, but the reason why you don't see each frequency shooting emitting from the cavity at different times is because it's either a continuous laser, or because the energy spread between the different colors is much smaller than the energy of activation to escape the cavity.
In either case, an analogy would be to place multiple crystals stacked together into one laser, and stimulating all of them. If you assume that there are no diffraction problems, and that they all emit at roughly the same period, you have a very crude multi-chromatic laser.
GPL Deconstructed
These aren't exactly new, but this is a new(ish) way of getting larger bandwidths. Before you have been more limited by the physical properties of your material, which meant you had to use interesting carcinogenic dyes, or expensive crystals to get broad stimulated emission cross sections.
I'd publish my course notes on the issue, but I'm not certain my prof would be too happy. I'll check with him when I see him Monday.
-Yarn - Rio Karma: Excellent
Argh. It seems there is one of those unwritten Slashdot rules that dictates any story about lasers must be accompanied by posts about laser weapons... usually in the Death Ray variety. For the most part lasers make poor offensive weapons, at least in the Burning a Hole Through X variety.
(Thank you Alien54 for not suggesting such a thing)
I've posted this before but here it is again:
***************
It seems inevitable that whenever there is a story regarding lasers we get to see all sorts of silly posts about blasting people with laser.
Even antimissle lasers have a long way to go. Between power requirements, beam handling, divergence, and atmospheric interference, lasers do not make great destructive weapons.
However, they would be damned good for some nasty tricks like blinding the enemy army (or, unfortunately, civilians).
Take this scenario: a bomber/cargo style aircraft has been outfitted with a large infrared laser (similar things have been done). Fly said aircraft over the people you wish to 'zap'. Release some fireworks or other attention getting devices and when the crowd looks up turn on and start scanning the laser.
Since the laser is infrared nobody would know they are being exposed to blinding levels of light, nor would the blink/aversion reaction take place. By the time you noticed anything the permanent damage has been done. Scary huh?
Another scenario under serious consideration by police (at least here in Canada, I've participated in meetings on the subject) is the use of lasers against commercial aircraft. The idea isn't to shoot down the aircraft, but to scan at temporarily blind the pilot during final night approaches. The effect is like someone flashing a camera flash in your face when your in a dark room.
As the few moments prior to landing are the most critical, distracting and flash blinding the pilot could easily lead to the plane crashing.
Worse, new solid state lasers are available in the 3watt (plenty of power to cause permanent blindness) range and can be powered off a car with an inverter. Simply park at the end of a convenient runway at night, plug 'er in and away you go. Ok, so it's not quite that easy, but the concept is...
Doesn't that all just scare you a bit more than some silly death ray?
Note: after saying all that I want to point out that I do not support the insane regulations placed against the use of lasers in the United States by the CDRH. It's totally ridiculous and overzealous.
"They do not preach that their god will rouse them, a little before the Nuts work loose." Kipling, 'The Sons of Martha'
If they can make them powerful enough, I can imagine this being used in laser target designators to make them more immune to changes in the absorption properties of the atmosphere. Also, a lot of FSU tanks have optional laser warning receivers, which might not pick up this "spread spectrum" laser.
Comments, anyone?
Score:-1, Wrong
I can't see it being simple to modulate the laser to do that, but generally modulating the laser isn't much good for high bitrates.
The trouble is the very power modulation can cause shifts in frequency (due to ohmic heating), leading to unwanted losses and cross talk.
Better to have an external modulator which can change its loss at various frequencies, and use this as the source.
-Yarn - Rio Karma: Excellent
For me the device that they build is a way to have multiple lasers in the same packaging, each with a slightly different wavelength.
Each of the individual emmiting layer is monochromatic and coherent, but the resulting beam isn't, you're right.
What would be interesting is to see a diagram which would give the intensity of the light for each wavelength.
I suspect that it isn't totally flat, but more something like this:
/\/\/\/\