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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.""
Does that mean we're half way there to light sabres? ;)
Egads, someone find Gordon, and find him quick! I don't want to be a slave to some bigheaded multidimensonal being! (Bill Gates is bad enough)
Pardon my ignorance (it's been a very long time since my last physics class) but aren't lasers *SUPPOSED* to be monochromatic? I thought one thing that characterizes a laser is that all the photons are in the same phase. It must be a limitation of my imagination but how can this happen if you have multiple wavelengths?
Can someone who know more tell me what's going on here?
Never attribute to stupidity what can be construed as a monopoly preservation tactic.
I always thought that the whole point of a laser was that it was generating a perfect coherent waveform, so is this new laser generating light at a large number of wavelengths in the infrared, or is it an infinite number of wavelengths in the range specified?
Also, it seems like it would take a lot more development to extend this wideband laser work for something more consumer-oriented, like room lighting, as the light would need to be relatively omni-directional, which it doesn't seem like lasers are very good at producing now.
Sounds like the 1 electron processor from Signal to Noise. I wonder if anyone has a simple explanation of how it exactly works? It seems that the electrons build up so much energy which pentrates diffrent strata of semiconductors and that creates the diffrent wavelenghes. Is that anywhere close to right?
I wonder if this would have applications in optical communications?
It's not clear if the different wavelengths have to appear together, or can be manipulated individually.
If they can be manipulated individually think of the coolness.
So many questions.
"Peace, Love and Apathy"
I'm not sure I understand.
If in a laser the photons *had* the same phase, then their amplitudes would add up linearly. Since energy is proportional to the square of the amplitude, the energy of N "in-phase photons" would be N^2 times the energy of one photon, violating conservation of energy.
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";
The laser does not produce an infinite amount of wavelengths. Each layer produces one dominant wavelength, and one to several weaker wavelengths.
As for consumer applications, don't hold your breath. Unless these are cheaper to produce than your supermarket price-checker, they'll stay in the realm of science for now. Multi-spectrum lasers are useful simply because they're light that all goes in one direction, which makes them useful for observing molecules.
Of course, they don't mention the weapons potential
or laser headlights for *really* bright high beams on the car.
"It is a greater offense to steal men's labor, than their clothes"
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.
if you isolate consciousness, lasers would be directly operated by the concious brain.
-- Hexadecimal.
The whole point of a laser is to get an intense and highly directional beam of light. The reason for this would be for coupling to an optical fiber or other such application. Also, since the energy density of the spot would be auite large compared to an LED, you would never want to use it as a light source. The naked eye would be damaged.
"It's comin' back around again..." -RATM
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'
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
Researchers at MIT have already moved on to more advanced technology. With cascading, the laser accelerates the nanodes in the visible spectrum to get its "beam" effect. Obviously, this is a huge drawback because of the excess power consumption wasted on acceleration.
Professor Warton, whom I work for, has implemented a prototype "Quantum Tripoly" laser. "Tri" because it uses three quarks rather than one and "poly" because it's basically 3^3=27 quantum cascade lasers in one. And there's no acceleration downside that I mentioned above, no waste, just laser goodness.
The future isn't cascading, so why is Lucent still working on this dead-end technology?? Anyone with a PhD in physics care to comment??
Its not actually true the theres always only one wavelength per substance- even single atoms like copper can emit multiple wavelengths
Imagine a Beowulf cluster of th... oh never mind.
But Maaa! Everyone else has a
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
"In any quantum-cascade laser, a high voltage coerces an electric current to penetrate layer after layer in the stack. The tight physical confinement of many of those stacked layers makes them act as so-called quantum wells, in which electrons can only have certain amounts of energy,..." Anyway it was good for me :-) and now I have to go and smoke something. The future's so bright I have to ware shades.
heuristic algorithm seeks stochastic relationship
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:
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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'
Jedis use Argon in their lightsabers, and the Sith use Krypton or Helium Neon ion gas in theirs.
my pet machine
"Here, let me try this new gizmo out by beaming these MP3s over to ya. Just line up your comp. right next to mine."
[Star Trek phaser sound]
"Wow! that was the fastest transfer I've ever seen!!! Sorry about the big hole in your computer though.."
In a society that believes in nothing, fear becomes the only agenda ~ Bill Durodié
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
Do they really have a polychromatic laser or is it just a laser that allows the user to choose an arbitrary wavelength in a given range? The article explains how they get spontaneous emission with a wide range of wavelengths, however it does not explain how to build a cavity that keeps a polychromatic wavepacket (wide in the momentum space) in a stationary state.
I had the chance to play with a 200mW Argon laser last year. It can laze at many different wavelengths, but i can set the cavity only to a discrete set of wavelengths. This was crucial for deciding between the 351.1nm and the 351.4nm (iirc) line. *g*
This sig is a true statement, but I cannot prove it.
Lasers are very good at producing omnidirectional light.
Pop the columnating lens out of a laser pointer to see just how omnidirectional it is (and please don't look right at it). It's just like any other light source in that respect.. the only difference is that the light it produces is of one wavelength, and in-phase. Both reasons why it's not an ideal room light. But direction has nothing to do with it.
Lasers are focused using a columnating lens.. just like any other light.
As the article said... this produces laser lightevenly distributed across the mid-infrared range.
Is that like wearing a red hanky on the right?
For better or worse (to it's employee's)
I should do some calculating, before i post.
If L is the length of the cavity and l is a wavelength, then the distance of the next wavelength that has a resonance in the cavity is l^2/L and this is VERY small under usual circumstances. I think i should read something about laser basics.
You are right, thank you!
This sig is a true statement, but I cannot prove it.
Also, it seems like it would take a lot more development to extend this wideband laser work for something more consumer-oriented
The point of this is not for a general consumer device any time soon. This device will be used in spectroscopy where there are very few line source lights that operate in the mid-infrared range.
My TV already came with a remote control.
Donate background CPU time to fight cancer.
Hmrr, parent post is a valid question and deserves a proper answer.
Lasing phenomena occurs in some media if you have so called "inverse population" of metastabile states of molecules. "Metastabile" means that those (excited) states cannot de-excite in to the lower energy level by spontaneous photon emission (e.g. momentum conservation forbids singlet-triplet transitions). However, if such metastabile molecule is hit by the photon with the energy that corresponds to the difference between upper and lower energy level of the molecule, a stimulated emission occurs. Emitted photon has the same wavelength, phase and direction as the incident one. In the conditions of inverse population (lots of metastbiles and sparsely populated lower levels), something similar to chain reaction happens. The initial photon gets multiplied in the geometric progression as it propagates trough the medium. This accounts for "Amplification" in the acronym LASER. In many cases upper and lower energy levels are well defined i.e. discrete, but they can be energy bands or even continuum. In the later case the wavelength of the "triggering" photon can lie in the range of values. This is actually the answer to the parent of this thread.
The lasing medium is usually confined in so called resonant cavity consisting of parallel mirrors. The reason for this is to effectively enhance the length of propagation in one preferential direction. The bunch of photons are bouncing back and forth between the mirrors many times and each time they traverse medium their number is increased. One of the mirrors is somewhat transparent and the portion of the beam exits the cavity.
... why is a laser pointer more useful for directional things than a simple flashlight? After all, an incandescent flashlight is simply an omnidirectional light source with a broad frequency range, roughly focused with a (usually cheap) parabolic reflector. Why could a flashlight not produce as potent and well-focused beam of light with the same colimating lens? After all, you can build a very cheap arc lamp that puts out thousands of watts of light. If you could focus THAT on a small spot, it would be as hot as the arc that produced it in the first place. So what's the problem with doing that?
(This is a serious question. I'd love to hear the answer from a qualified physics type. I'm even willing to burn a karma point to show this at a 2 rating, so I stand a chance of getting a real answer.)
I'm just guessing, but it's probably because the monochromatic nature of most laser pointers means that ALL the light focuses the same thru the collimating lens. This is of course because different frequencies of light have different refraction angles thru a lens. Therefore, with a broad-spectrum source like a light bulb, you cannot sharply focus the beam, because each frequency focuses at a different place. As I write this, it occurs to me that's why a flashlight uses a parabolic reflector - because reflection is not affected by wavelenght like refraction is. But with a parabolic lens, the fully parallel beam can never be smaller than the diameter of the lens.
--Brandon / Split Infinity Music
First off, I'm not a physicist. It's been years since "Physics for Engineers" and I didn't even do very well in that course... (Though I would fare better now, as my calc skills have improved vastly!)
That having been said... That PDF is quite a document! It seems very comprehensive -- is it something you put together, or was it given out by your professor? (If so... God! Wish I got PDF handouts in my day!) I did note the creator info, but "Ian Clark" doesn't mean anything to me. All that work using LaTeX, too!
Impressive. Thanks for the posting it!
"...America's great minds of today, teaching America's great minds of tomorrow. Poor bastards." -- A Beautiful Min
If we could channel the energy of a matter-antimatter reaction into these polychromatic lasers, then we would have an effective phase cannon. Instead of throwing away the energies in the other wavelengths of light, these polychromatic lasers use all the wavelengths and combine them into a beam of sufficient power to send a bird of prey to Stobelcore!
I'm going out on a ledge, but I'd believe one of the major applications of this is in DWDM down single mode fiber. It simplifies manufacturing costs to have a laser that can output on different wavelengths vs. multiple lasers all specifically designed for a single wavelength. I was reading a telecom book today at Barnes and Noble that pointed to that specifically as one reason for the current high costs of DWDM. Of course I have to take the book for a grain of salt considering it was yellow and black :).
white led's have been around for a while now. last i heard, their principle of operation was laser physics - for the monochromatic ones anyway.
Besides, there aren't an infinite number of wavelengths in between. Light can only certain wavelengths, as described by the laws of quantum physics. If this weren't the case, every light source would be putting out an infinite amount of energy.
It's all from my notes of a lecture course. No handouts.
-Yarn - Rio Karma: Excellent
Lasers operate on the priciple that an atom 'detects' a wavelength of energy going by it that it happens to be holding, and releases it in the same phase as the other. Repeat X1000^2. Voila, laser light.
The beam gets repeated by two parallel mirrors, one is opaque, the other is part-way(leaky), which lets the light out, lasing maerial between.
Replace the opaque mirror with a prism, which spreads the spectrum out, pick a color and place a mirror perpendicular to the beam, and it will reenter the lasing material. The stimulation will reinforce the one color, and the others will degrade(filters would reduce the frequency you want due to imperfections), works with multiple frequncies.
What should be really fun would be a EL-display type laser device, which might be tunable with the voltage across.
(As far as rude colors, ever see a neon *plasma* pink?)
This mind intentionally left blank.
The KKK a bunch of sheetheads? You decide!
Why am I smacking my forehead. I should be smacking yours. Basically, now they have a laser that can replace the 10 or so lasers that would normally feed an optical fiber. Now they can make things smaller and fit more stuff in those central offices at the phone company and stuff.
Before I mouth off, I should research the terms I'm looking for. Also I should get some sleep.
If Mr. Edison had thought smarter he wouldn't sweat as much. --Nikola Tesla
MIDIfrared? Let me know when we get to OGGfrared, then I'll be more interested.
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"Outlook not so good." That magic 8-ball knows everything! I'll ask about Exchange Server next.
I was fairly certain that glass prevents most of the harmful radiation in the ultraviolet spectrum from damaging your eyes, so for example, you can watch a nuclear explosion from your car without permanent blindness. Does this work with infrared as well? Because if it does, that would cancel out any problems with aircraft -- or people with glasses.
So what we're looking for, then, is a device that emits light in many different wavelengths and in all directions. Do I see any light bulbs appearing over people's heads right now?
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Sorry, I'm only a 1336 h4x0r.
I suppose they need to update Austin Powers now.. "Mini-me! Stop humping the polychromatic LASER"