Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
Contents may be not!

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.



Hyper Lasers

A new way to amplify light?
  (+9, -2)
(+9, -2)
  [vote for,

Inside an atom, when a passing photon encounters an electron, there are several possible outcomes. If the photon is the wrong frequency, the photon may continue on its way, no interaction occurring at all. If it is the right frequency, it may be absorbed by the electron (which jumps into a different, more energetic, orbit around the atom). And if another photon of the right frequency comes along, and encounters an electron in that more-energetic orbit, well, then this new photon KNOCKS the electron back down to a lower-energy orbit, and causes the previously-absorbed photon to be emitted.

Quantum Mechanics precisely describes the details of electron/photon interactions, to an accuracy that so far has been entirely verified by experiment. The particular effect of one photon knocking another loose from an electron in an energetic orbit is known as "Stimulated Emission of Radiation". And, since now there are two photons where before there was one, we are also describing a "Light Amplification" effect. And so certain gadgets have their operating principle described by those two quoted phrases, while the five capital letters yield the gadget's name: "LASER".

The question of the moment concerns whether or not SER can be a more generic thing than something requiring electrons and their orbits about atoms. Part of the answer is YES: There is a device known as a "free electron laser", which uses electron beams in a vacuum, and an array of alternating magnetic fields.

I wish to describe what might be another variety of free electron laser -- or, rather, a "free electron light amplifier". This device does not have the purpose of generating a laser beam; it has the purpose of vastly intensifying an existing laser beam. If it works at all, then it may work at near-100% efficiency!

To begin, it is necessary to examine the environment of an atom in a little more detail. As you probably know, the atomic nucleus is surrounded by an intense electric field, the intensity of which diminishes with distance away from the nucleus, in accordance with the inverse-square law. It is not unusual for electrons in an atom to move through a region where the voltage field has an intensity-drop of four volts per Angstrom. (That is, if at Point A, located some small distance from the nucleus, the electric field has an intensity of X volts, then at Point B, located a ten-billionth of a meter farther from the nucleus, the voltage-intensity is X-4.)

In such a region, if an electron makes a quantum jump across half an Angstrom of distance, then it will either be radiating, or be in the process of absorbing, a photon having two "electron volts" of energy. (Such a photon is visible to humans as perhaps yellow-orange in color.)

Now normally the reason why an electron might make a half-Angstrom jump is because that is how a particular atom happens to be put together: a half-Angstrom jump is ALLOWED, but perhaps not a full-Angstrom jump. Well, what if any size jump was allowed? Would the electron still jump if knocked by an appropriate photon? Here's how to find out:

Start with a vacuum chamber, and place two needles quite close together, pointing at each other, with perhaps a micron (a millionth of a meter) gap separating them. Prepare some lenses so that a laser bean can be focused exactly in the gap, and straightened out again. Now turn on the laser, and apply 40,000 volts to the needles....

It happens that a voltage spread of 40,000 per micron is the same as 4 volts per Angstrom. We are most certainly going to get a whole lot of electrons leaving one needle, and heading for the other. If no laser beam was present, those electrons would simply and smoothly accelerate until they smashed into the other needle at a fairly high velocity. BUT I have specified that the laser beam is ON. What happens now?

Each electron HAS THE POTENTIAL to make small quantum leaps. Each electron has a large probability of interacting with a passing photon. Each electron exists in an electric field that is rather similar to the electric field surrounding an atom, where quantum jumps are normal and ordinary and downright common.

WHY SHOULDN'T each electron, INSTEAD of accelerating smoothly, simply get KNOCKED again and again and again, making quantum-jump after quantum-jump, all the way across that gap, NOT ACCELERATING AT ALL, BUT INSTEAD EMITTING PHOTONS. Those photons, of course, would increase the intensity of the laser beam! A LOT!!!

If this idea works, then we could prettly easily make stages of amplifiers that turn kilowatt laser beams into gigawatt or terawatt laser beams, and thereby we become able to do inertial-confinement fusion easier, or to shoot down ICBMs, or to launch payloads into orbit more cheaply....

Vernon, Jul 22 2001

Interaction of light and matter... http://www.chemistr...ontent/light-ma.htm
...courtesy of the University of Adelaide. [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

Interaction of light... http://ajdubre.trip...niverse-SZ-301.html
...and free electrons in supermassive galaxy clusters. [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

Interaction of laser light... http://www.scienced...12/981218080014.htm
...with free electrons in a superheated plasma. [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

(?) LOTS of needles in a vacuum http://www.candesce...escent/tcrtcnpt.htm
A flat-panel display under development....(the needles are called "emitter cones") [Vernon, Jul 22 2001, last modified Oct 21 2004]

(?) Boost laser light... http://inisjp.tokai.../ACT00E/01/0103.htm
...with electron beam! Japanese lab using Compton scattering of laser light to produce high-energy gamma photons. Nice site. [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

(?) ZEUS experiments... http://www-zeus.des...l2000/laserwid.html
...at Hamburg are hitting electrons with lasers. [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

Lawrence Livermore labs... http://www-phys.lln.../LaserElectron.html
...is aggressively pursuing laser-electron interaction research. [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

Indian Laser Association's... http://www.cat.erne.../ln971/thomson.html
...semi-technical description of scattering of photons by electrons. Um, there's a bit more to it than is thought of in my summary, Horatio... [Dog Ed, Jul 22 2001, last modified Oct 21 2004]

Solid Lightswitch http://www.lightrea...eading&doc_id=10998
Description of a photonic alarm clock for zero speed light [reensure, Jan 19 2002]

Spectroscopy http://www.woodrow....chem1/Chapter4.html
Everything except how lasers work [Vernon, Oct 04 2004, last modified Oct 21 2004]

"Simple" laser equations http://jchemed.chem...m/mcad016/laser.pdf
Some stuff that is more advanced than what I was looking to link. [Vernon, Oct 04 2004, last modified Oct 21 2004]

Laser Basics http://www.phy.davi...er-Final/opener.htm
This looks like good background information. [Vernon, Oct 04 2004, last modified Oct 21 2004]

Inside a Tunnel Diode http://mxp.physics....ects/menz/paper.pdf
Phonon and Photon emission [Vernon, Oct 04 2004, last modified Oct 21 2004]

Something that Needs Efficient Lasers http://www.halfbake...eactor_20Variations
Gratuitous Link [Vernon, Oct 04 2004]

Quantum Cascade Lasers http://www.rp-photo...cascade_lasers.html
[octal40, Mar 02 2007]

Electron Orbitals http://www.orbitals.com/orb/
look at the pretty shapes ... [octal40, Mar 02 2007]

Quantum Tunneling http://en.wikipedia...i/Quantum_tunneling
wikipedia ... [octal40, Mar 02 2007]

National Ignition Facility laser http://www.llnl.gov...ject/nif_works.html
Follow the "amplifiers" link on that Web page for more details. [Vernon, Mar 05 2007]

The Ghostly T.O.E. http://nemitz.net/vernon/GHOSTLY.pdf
Some stuff about Quantum Mechanics, as mentioned in an annotation. [Vernon, Mar 09 2007]


       I don't know whether this would work but I'm all for bigger lasers...
RobertKidney, Jul 22 2001

       Vernon, this is quite technical and I ain't no physicist. That said, here are some thoughts off the top of my head:   

       In the atomic regime, electrons absorb and emit photons of a particular wavelength because atomic electrons inhabit quantized electron shells. In the free electron stream between the two needles, how will the electrons "know" to absorb and emit photons of the same wavelength as the incident light? Put another way, an atomic electron stores the energy of an incident photon by moving to a higher-energy quantum shell--but what is the analogous energy storage mechanism for a free electron interacting with a photon of incident light? Might the electron simply scatter the photons randomly, destroying the coherence of the laser beam? (I dunno the answer--I'm asking, not telling!)   

       I suspect that in a vacuum you need to use an electron gun, ie a cathode made of a substance which emits free electrons when excited, to get a flow of electrons. But that's relatively trivial adjustment to the setup.   

       Personally, I don't get the part about quantum jumps versus smooth acceleration. On the subatomic particle level, there isn't any smoothness, is there? Isn't all movement and acceleration quantized--reduced to a probability of finding an electron here or a Planck's distance or so away instead? So the laser beam doesn't alter the way electrons move between the cathode and anode, in that they already proceed in a quantized manner.   

       It seems that the point is to convert the voltage potential across the cathode-anode gap to photons of a particular wavelength--to convert the kinetic energy of the electrons, which would otherwise accelerate across the gap--into coherent light. Is that a fair condensation?   

       Jeez. I gotta go look up photomultiplier tubes and some other stuff. Nice one, Vernon--I'll vote for it just 'cause it's interesting even if it isn't practical.
Dog Ed, Jul 22 2001

       Here's an excerpt from a Science Daily article which deals with Thomson scattering of light by free electrons. I'll add a link to the full text in a minnit.   

       "In the experiment, which was designed to test basic aspects of electrodynamic theory formulated over the last century, the researchers focused one of the world's most powerful lasers onto a supersonic jet of helium. The laser---with a power of more than a trillion watts---ionized the atoms of the gas, creating a plasma composed only of free electrons and ions."   

       "The U-M scientists then discovered that the electrons scattered the laser light into colors (frequencies) that differ from, but are harmonically related to, the original beam. Furthermore, the angular direction of the scattered light was observed to be unique to each harmonic. This is the definitive signature of electrons moving in figure-eight patterns due to the combined forces of the light's electric and magnetic fields. The observations were recorded with a digital electronic camera and various filters."
Dog Ed, Jul 23 2001

       Dog Ed, the primary reason for posting that idea is to encourage someone with the resources to try the experiment and find out! So, with respect to your questions, I can't offer a lot of hard data....   

       How might an electron "know" what frequency of light to emit, when a photon knocks it while in-between the needles? Well, Interactions According to Quantum Mechanics are peculiar things. One might go so far as to say that whenever Particle A interacts with Particle B, some "connectivity" can remain even after the particles separate by significant distances. I tend to think that the "imprint" of the photon on the electron, during the interaction, is what would tell the electron how far to jump, to yield an identical photon. I do recognize that the jump has to be "reasonable", in terms of voltage-gradient and the natrual limitations of an electron's abilities to perform quantum jumps.   

       The "storage mechanism" is, in this experiment, not a quantized thing. It is an entire reservior of potential energy, represented by the (40,000V) voltage-difference between the two needles. An electron alone in the gap between the needles will draw upon that reservior in order to accelerate; AND, YES, it will emit some photons simply because accelerating charged particles always emit some photons --so it seems reasonable to me that the electron can draw upon that reservior to emit a photon in accordance with a "knocking" photon.   

       The "scattering" of light is just another word for "reflectance". IRREGULAR reflectance, usually, but reflectance all the same. Now since many substances are transparent, it is obvious that scattering is not a guaranteed thing. I suppose the experiment will have to be done before we know the answer to that.   

       No, an electron gun is not required. 40,000 volts is plenty sufficient to cause a spark THROUGH THE AIR, across a distance far greater than a micron. Now of course that works because the voltage breaks apart some of the air molecules in the gap, leaving a conductive pathway. But a vacuum IS a conductive pathway!   

       Yes, there is little smoothness at the subatomic level. Nevertheless, for some things, like electrons accelerating in a uniform electric field in a vacuum, across macroscopic distances like a micron, Newton's smooth equations are adequate for most of the task. Only the part about how accelerating electric charges naturally emit photons needs to be tweaked into the description. The level of quantized detail that you mention simply is not needed very much.   

       However, when the laser photons are added to the mix, THEN things become wild and wonderful, and the descriptions of Quantum Mechanics reign supreme. The goal of the experiment is NOT to convert an electron's kinetic energy into photons, it is to convert an elctron's POTENTIAL energy into photons. Inside the gap between the needles, an electron can either accelerate for a small distance and acquire kinetic energy, or make a quantum jump across that same distance and emit a photon in the process. In the second case the photon will contain the same amount of energy as does the electron in the first case. The ideal goal of this experiment -- if it works at all -- is to encourage a zero-velocity electron JUST LEAVING one needle to arrive at the other needle STILL with zero velocity, having made photon-emitting quantum jumps across the entire width of the gap. Almost certainly, only in theory can we think of this experiment truly reaching 100% efficiency like that.   

       Concerning the experiment you describe in your other annotation, it might be noted that the electrons in the plasma were simply THERE; they didn't have energetic business to attend to, OTHER than to mess up the photons in the laser beam. I am hoping that the influence of the voltage gradient has rather different consequences.
Vernon, Jul 23 2001

       Well as usual I am feeling my way into the topic and making mistakes. I think, though, that you need an electron emitter to get an electron flow in a vacuum--that's why vacuum tubes use tungsten, tungsten impregneted with thorium oxide, or various alkaline-earth coatings on nickel alloy wires for the cathode and not just any old needle. ;)   

       I'll bet that the behavior of photons scattering off electrons is the crux of the biscuit here. There are pretty well-defined interactions possible: absorption, Thomson scattering (electron absorbs photon, emits a similar photon), Compton scattering (electron and photon collide more or less elastically, with electron recoiling and emitting photon(s) of varying wavelength), and pair-production (photon and electron collide with such energy that a positron-electron pair is created). I've listed the modes of scattering more or less in order of ascending energy. (Oh, I'm using "scattering" here in the physics sense of "an interaction between subatomic particles other than simple absorption." It's technically incorrect to think of photons as simply reflected from an electron; on the quantum level the electron absorbs the photon, is thereby excited, and the energy of its excitation is dissipated by formation of an electromagnetic wave-packet--ie the emission of a photon.)   

       Arg. Like the Straw Man, if I only had a brain...   

       I'll try to get a comprehensive overview of the modes of photon scattering off electrons. Fascinating stuff.
Dog Ed, Jul 23 2001

       I am an idiot about this (and many other subjects) but I must ask: are there not already all-optical amplifiers for lasers in use within fiber-optic systems? Erbium doped fibers with another laser to optically pump the doped fiber, and amplify the laser as it passes through?

I'll hang up and take my answer on-the-air . . .
bristolz, Jul 24 2001

       Dog Ed, there are two reasons why electron guns are most commonly used in vacuum devices, such as CRTs. First is the voltage level -- sure, several thousand volts are used, but that is a LOT less than the 40,000 proposed here, AND the distance across which the voltage in a CRT is applied is very much greater than the single micron proposed here. Second, a flat or curved piece of metal (such as the spiral of a filament) is simply not a good electron-emitter, unless heated. But the sharp point of a needle IS a good emitter, even at rather low voltages. See the link I added.   

       Again, with respect to scattering, all such cases involve electrons that are NOT in an environment that encourages them to accelerate. Therefore the experiment needs to be done!   

       bristolz, yes, there are indeed optical amplifies that work on the laser principle. However, they are EITHER not much more efficient that the laser-generating-process itself, because they must hold a "population inversion" while a continuous laser beam passes through, OR they are only good for efficiently amplifying short pulses of light. If the idea suggested here works, we could have high-efficiency AND continuous beams.
Vernon, Jul 24 2001

       Vernon: You posted while I was still turning pages and scribbling... :) Nice link to the Candescence site, but the company itself calls those needles "emitters" and "cathodes," and I would wager a small amount of pastry that they use a high-tech electron-emitting substance analagous to the old tungsten-thorium cathodes. Sounds like they operate at low temperature...and maybe like Candescence would rather not tell us exactly what they're made of? I don't blame them! Cool technology.   

       [Later: "Tetrahedral amorphous carbon" has promise as a cold-cathode electron emitter. So, apparently, does some sort of synthetic diamond. Stay tuned...] [OK, diamond coated with boron nitride.]   

       bristolz: Yeah, you're completely right. Those U-M guys mentioned above, with their trillion-watt laser, pumped it up pretty hot with existing technology. This idea proposes a non-standard method of doing the same thing.   

       But I don't think it would work.   

       1. The energy for the photon-electron interaction is determined only by the combined energy of each particle.   

       2. You cannot extract potential energy from anything (it's like eating a sandwich today that you will not make until tomorrow). You cannot capture the potential energy of a coconut sitting at the top of the Eiffel Tower; only once it has fallen and gravity has accelerated it can you capture it's kinetic energy. Likewise, you cannot capture the energy of an electron before it has been accelerated. If there is any experimental evidence to the contrary, speak up.   

       3. Interactions between a (visible light) photon and an electron before it is accelerated will be of the low-energy sort well described in physics texts (unless the laser itself is so powerful it creates an electromagnetic field causing the electrons to vibrate as described by the U-M researchers.)   

       4. Interactions between a photon and an electron while it is accelerating across a voltage potential will depend on the total energy of the collision, again well-described in the literature. The wavelength, angle of scattering, and electron recoil for medium-energy collisions, ie Compton scattering, can all be calculated algebraically.   

       5. If the electron is accelerated tremendously, to a large fraction of the speed of light, then collisions with an aggregate energy > ~10MeV will sometimes produce a positron-electron pair. The positron will of course annhilate with a nearby electron, releasing a burst of radiation.   

       I don't think there's anything in this setup which will result in extraordinary amplification of light.   

       Most of the info on scattering comes from "Fundamentals of Physics" by Halliday and Resnick.   

       [yet annother addendum: I'm certainly in favor of messing about with electron beams and lasers, Vernon. If I had the equipment and expertise (and money!) I'd do it in a heartbeat, and some research facilities (TESLA and a Japanese facility) are doing it, albeit at very high energy. And...on another posting I speculated on the interaction of photons with a transparent material travelling at near-lightspeed, then emailed the problem to a real physicist...and my speculations were *way* wrong. So there is an excellent chance thay my speculations here are equally wrong. But whatever the outcome, I've spent the last couple days researching and trying to understand electron-photon interactions; I've learned a lot; and I've been able to add some new information to the Materials For Techno-Wizards part of the Halfbaker's Helper. Thanks!]
Dog Ed, Jul 24 2001

       Dog Ed, you might notice that neither did I specify what sort of material the needles in this experiment should be made of. The POINT is simply that a needle WILL emit at low temperature, given sufficient voltage. If just one ampere flows across the gap, and this mad idea actually works, then the beam of light could be boosted by (say 50% efficiency) 20,000 watts. Of course that's not good enough!!! The RECEIVING needle will be destroyed if it has to catch the OTHER 20,000 watts! So I am very aware of various possible problems with this idea.   

       Next, while ORDINARY electron/photon interactions are indeed completely determined by the energies of the particles, those are NOT the only factors present in this experiment. DURING this interaction, the electron IS immersed in a high-voltage electric field, and it WILL be influenced by that field, in some fashion. Only the details of that influence, and its consequent effects on the electron/photon interaction, are under discussion here.   

       It is possible that I used poor phrasing with respect to "extraction of potential energy". CONVERSION is a better word than extraction. The potential chemical energy of coal and oxygen is converted to heat and light when burned, for example. In this experiment the voltage gradient between the electrodes gives electrons the potential to accelerate, and under ordinary circumstances they will indeed do exactly that. The experiment is to find out whether or not that potential can be converted into light, instead of acceleration. AND, with respect to an electron inside of an atom, when located in a "high" orbit it has the POTENTIAL to jump down to a "lower" orbit...and when it does, its actual orbital velocity changes very little; instead the potential-energy-difference, between the two orbits, will manifest as a photon. So in this very common case, the energy of the electron IS captured "before it has been accelerated". The energy appears as a photon INSTEAD of acceleration. The low-electron-energy interactions of the UM researchers MIGHT be relevant to this experiment whenever the intense electric field is OFF. However, whenever the field is off, there are no electrons in the vacuum for the light to interact with! And when the field is ON, we suddenly have an environment similar to the interior of an atom, where quantum jumps are normal.   

       Since the goal of the experiment is to find out whether or not the electrons between these needles will make quantum jumps INSTEAD of accelerating, BECAUSE of interactions with photons, the well documented stuff in the literature is not especially relevant. Accelerating electrons are NOT wanted here!   

       An electron accelerated under the influence of 40,000 volts for one micron will not be travelling at any significant fraction of light-speed. In fact, I'm beginning to wonder if I haven't made some fundamental calculation error, regarding how an electron manages to be involved, in the emission of a 2-electron-volt photon, in the first place. Perhaps an electric field significantly larger than 40,000 volts will be required.   

       As a variation on the experiment, consider the narrow laser beam emited from a diode: If this experiment was modified so that the needles were replaced by two long long razor blades had their edges lined up, and the laser beam went lengthwise inside/along that gap, how much power might be added to it?   

       And you are quite welcome, to the thought-provocations that I try to offer here, heh heh heh....
Vernon, Jul 26 2001

       //...instead the potential-energy-difference, between the two orbits, will manifest as a photon. So in this very common case, the energy of the electron IS captured "before it has been accelerated". //   

       Well, I would disagree: the energy emitted by an atomic electron dropping from a high energy orbit to a lower one is real, not potential, energy. Add energy, boost the electron to a higher orbit; get energy back when it drops to a lower orbit--nothing mysterious there. The energy isn't straight-line-momentum kinetic in this case, it's vibrational [addendum: not literally vibration, but kind of analogous to it in that the electron in a higher orbit has a differently-shaped and/or larger probabilistic area to thrash about in] but the electron still has to gain that quite real energy before the energy can be captured.   

       The hyper-laser is an interesting idea, and certainly there's a lot of work being done with accelerated electron beams and lasers. Seems to me I surfed across one website that mentioned a possiblity of glimpsing the Higgs boson in a photon-electron interaction (at very high energy, of course). I'll see if I can find a few of the active research sites and post links.   

       [Later: Posted a lot of links. Most of the action seems to be in producing higher-energy photons (x-ray and gamma ray) by hitting highly accelerated electrons with laser light--the Compton scattering I've mentioned. Given the technical sophistication of these efforts I would bet that if you looked hard enough in the literature you could come up with a report on an experiment like the one you describe.]
Dog Ed, Jul 26 2001, last modified Jul 28 2001

       Gentlemen, please know my appreciation for the scope of this exchange grows with each annotation. It's a fascinating subject and your treatment of it here is a watershed to one who has heretofore found the nuts-and-bolts of it all nothing short of daunting. Sincere thanks for your time and effort.
The Military, Jul 28 2001

       Well, I find that you can use capacitor plates to get a current to flow (intermittantly) through a vacuum. The capacitance of a vacuum is defined as 1.0, air is something like 1.0054, and dielectric solids and liquids go up from there. However, the table in the book showed arc-breakthrough energies for everything except vacuum and (pure) water--which seems to imply that you could never get an arc between two conductors in a vacuum. But I dunno. Like I said, I'm feeling my way along and learning as I go.
Dog Ed, Jul 31 2001

       Dog Ed, please note that if a sharp point is used on the end of a lightning rod, to make it easy for static-electric charge to leak off into the air, it follows that a sharp point in a vacuum, with a large negative charge on it (40,000 volts, remember), is going to emit electrons, no ifs, ands, or buts -- and no high temperature, either.
Vernon, Aug 02 2001

       From the Handbook of Chemistry and Physics, 61st Edition, here is the definition of the "electron volt": [Amount of] Energy acquired by any charged particle carrying unit electronic charge when it falls through a potential difference of one volt.   

       This relieves me of concern about a fundamental calculation error, as mentioned in a prior annotation. There is NO distance requirement! (I was vaguely thinking that the definition concerned an electron accelerating across a one-centimeter distance in a one-volt field.) Instead, ALL that matters is the one-volt potential difference. I am certain that the appropriate amounts of calculus will easily show that, thanks to the inverse-square law, if one electron accelerates in a one-volt field between two plates spaced 1 centimeter apart, and another electron accelerates in a one-volt field between two plates spaced 1/10 centimeter apart, then both electrons will accelerate at different rates, and end up with identical energies.   

       Thus there is no real flaw in my original description of the emission of a 2-electron-volt photon by an electron that jumps 1/2 Angstrom across a voltage gradient of 4. And THAT in turn means that the 40,000 volts suggested, with respect to the micron-sized gap between two needles, will indeed adequately simulate the innards of an atom, through which electrons normally and easily make quantum leaps.
Vernon, Aug 05 2001


       Two thoughts which might have have already been covered here, but there is a lot of text to read in the annotations. Firstly I wonder if you might be able to make use of entangled electrons to encourage state switching.   

       Secondly, the multi-needle in a vacuum principle is not that new-fangled. There is a patent going back to the 60's for vaccum valves (tubes) which used an array of fine points instead of a rare-earth heated cathode. I've never heard of it going into production tho.
tonywells, Jun 28 2003

       tonywells, state switching is not part of this laser idea, because the "high state" is represented by the electrons just leaving the cathode, and the "low state" is the plethora of half-Angstrom intervals beteen cathode and anode. If this device works as described, then all the energy that the electrons would acquire, in accelerating between cathode and anode, would instead be stimulated-emitted as extra (amplified) light, during the crossover between electrodes, at each of those intervals.   

       And, I didn't claim that the multi-needles idea is newfangled. It's simply one of the best tools available for the needed job, of getting lots of electrons into a vacuum, nondestructively.
Vernon, Jun 30 2003

       Hmm. Here is my stab. I don't think it will work. I suspect that any electrons jumping around the various bands in an atom (and emitting a photon) is a very different process from merely jumping the spatial equivalent between needles in a vacuum space. By operating, what is essentially, a spark across a vacuum of 'x' Angstroms I don't think you create any light.   

       (I'm sorry for not thoroughly going through the annos - I'll revisit when I have time)
Jinbish, Jun 30 2003

       jinbish, you really need to read the whole thing. (This is an amplifier, not an original source of light.) An ordinary spark does not significantly ACCELERATE, as it would in the portrayal here. The idea is to duplicate the electric-field gradient found inside atoms, between the electron-shells. The naturally Uncertain position of an electron means, even before it starts to accelerate, it is located almost-simultaneously at point A (high potential) and point B (lower potential, half an Angstrom away) -- and so a passing photon can "knock" it, causing it to quantum-leap and completely forget about existing at Point A, without having moved to B in the ordinary way. Since it didn't accelerate but did instead emit a stimulated photon, the electron at point B is now ready to repeat the event with respect to another photon and point C... all the way across the gap between the electrodes.
Vernon, Jun 30 2003

solo111, Sep 16 2003

       solo111, please use lowercase here, at least most of the time. Anyway, as you described, the frozen-light experiment relies on the presense of an abundance of atoms. (They absorb and hold the light.) Also so does your semiconductor notion rely on large quantities of atoms. Since this idea is pretty well restricted to the usage of a vacuum, it seems to me that what you are desiring cannot be done. The flow of quantum-leaping electrons that I describe is not going to appreciate having all those atoms in the way!
Vernon, Sep 16 2003

       thank you for pointing me in the right direction to go about building this laser so what you are speaking of can only work with gas filled chambers such as Nirtogen or helium gas to allow the 2 needles to emit (40,000v)is there a way to keep the photons in a higher state by using a emf to create more photons and emitting a ultrahigh-intensity pulse laser useing grating pair pulse streatchers? I would like to no more about how to implement your theory into a new concept for a lasers for deep space defence I am an Inventor and I don't have much background in physics but I understand the theories of physics and chemical element break downs I just have to find the right element to make the right reaction for the semicomductor? thank you vernon I will be back
solo111, Sep 17 2003

       solo111, the generation of voltage is independent of the presence of gas. It is simply that if you want to generate a spark across some distance through gas, then, the longer the desired spark, the more voltage required. Do note that a spark is a consequence of interactions between flowing electrons and the gas in their way. If the flow of electrons occurs in a vacuum, then there will be no spark. This is what I want, because a spark represents wasted energy. Next, the phrase "keep the photons in a higher state" is meaningless. An ATOM may have differing energy states, but a single photon always only has just one fixed quantity of energy. If absorbed, it is GONE. Each emitted photon can be considered "new", even if identical to an absorbed photon. You definitely need to acquire more fundamental information about atomic structure and photon-interactions. I recommend studying "spectroscopy" as the starting point. See link.
Vernon, Sep 17 2003

       ...Mad scientists are scarey... :) *throws a crossiant
Aerythes, Mar 02 2004

       Didn't read all the commens...but...   

       Electrons are electrons, how could they gain energy levels? aren't they descrete? In a laser, the excited matter (gas, etc) is used to store the energy and emmit the photons. How could a vacum support lasing, since nothing would exist to store the energy?   

       Wouldn't the needles diffract the laser beam quite a bit?   

       Wouldn't it be possible to fill a gas chamber with excited gas, then shine the laser through that? Wouldn't that act as a laser amplifier? I would think it should have extremely high efficiency, since the only power used would be to excite the unexcited gas in the chamber.
nomel, Jun 09 2004

       Lotsa time on your hands.
DesertFox, Jun 09 2004

       [nomel], "energy levels" are not a part of this Idea. I am merely suggesting that if an electon in an appropriately smooth voltage gradient is hit by a suitable photon, the interaction will cause the electron to make a quantum leap such that it can emit a photon identical to the impactor. Think of it as a kind of "quantum tunnelling" -- which does NOT necessarily involve atomic energy levels -- even though there is no barrier to ordinary acceleration. That is, with no impacting photon, the electron simply does some ordinary acceleration in that voltage gradient. WITH impacting photon, the electron is kicked into making a quantum leap. And the "stored energy" that you seek is provided by the SOURCE of that voltage gradient. You don't worry about where the electron gets its energy if it merely accelerates in the gradient, do you? So, if the electron is Kicked and Leaps and emits a photon, and ends up with NO velocity-change at a "lower" location in the voltage gradient, then why should you worry about where the emitted photon got its energy?   

       Regarding needles, In Theoretical Perfection, the passing photons are all supposed to miss the needles completely. The region through with the photons pass is supposed to be exactly as wide as the gap between the needles -- and not one whit wider.   

       Regarding gas, the inefficiency of lasers comes from the fact that excited atoms don't always wait for photons to come by to de-excite them. They spontaneously emit their "excitement" in random directions, and that energy is lost, as far as a laser beam is concerned.
Vernon, Jun 10 2004

       [Vernon], a very interesting idea, followed by a veritable battle royale between yourself and [Dog Ed]. For what it's worth, I would like to add my own $(1/50).

You say in your last anno that energy levels are not a part of this idea, and yet you talk about quantum leaps occurring. Aren't 'quantum leaps' inextricably linked to energy levels? You get a quantum leap when an electron confined within an electric potential moves to a lower energy level: this is because there are only certain discrete energy levels that the electron can occupy in that potential. This in turn is because the electron can only exist in a state in which one 'orbit' (although of course electrons don't orbit nuclei it's sometimes convenient to talk as if they did) must consist of an integer number of half-wavelengths.

My concern with your idea is that I don't think the electrons are confined. In fact they are moving freely, so there is nothing to restrict them to only certain energy levels. Hence, I think they are free to act in a simple billiard-ball like manner when 'struck' by a photon. So I see no reason why they should emit a photon at all.

Another point that concerns me is that I can't for the life of me see what would determine the size of the quantum leap, if it were in fact to occur. My (admittedly limited) experience of physics tells me that if you can't think of any parameters that would affect a phenomenon, then that phenomenon probably doesn't exist. But that's more of a gut instinct than a reasoned hypothesis: I wonder if you agree with me on that general point?

Anyway, well done for providing such a stimulating discussion. I have a sneaking suspicion that this idea just might work, but the second point I made above gives me doubts.
spacemoggy, Jun 10 2004

       [Vernon], are you thinking of Bremsstrahlung radiation? http://rkb.home.cern.ch/rkb/PH14pp/node16.html   

       If this were the case, then wouldn't the photon hitting the electron loose energy, since there wasn't excess energy to begin with, such as in normal lasing?
nomel, Jun 10 2004

       [spacemoggy], thanks for the feedback. Please note that in my prior anno that I referred to "tunnelling". Inside a tunnel diode, there are NO ordinary quantum energy levels, such as you find inside an atom. There is merely a potential voltage across an insulating region, which electrons are dared to cross. They effectively take on the dare by disappearing from one side of the barrier and reappearing on the other side -- tunnelling, that is, even though it can also be called "Leaping". Also, it is known that an electron that has tunnelled has also emitted a photon (see link, near top of second page; looks like inside solid matter it can sometimes emit a "phonon" too!) Please note that the voltage gradient in a tunnel diode is extremely small, relative to the voltage gradient inside an atom, and so the emitted photon has quite low energy.   

       Next, and getting back to the vacuum inside the proposed Free Electron Light Amplifier, remember that I have specified a very LARGE voltage gradient, quite equivalent to the innards of an atom. SURE, there are still no energy levels, and an electron is free to accelerate in normal fashion. Indeed, it is quite possible that they will interact with a passing photon as you suggest, in billiard-ball fashion. HOWEVER, because of the voltage gradient in which the electrons find themselves, they will have an overwhelming tendency to be drawn across the gap between the electrodes. Being struck by a passing photon will not change that simple fact, and I submit that the surrounding voltage gradient will give the knocked electron an OPPORTUNITY to make a quantum leap -- leaping is faster than accelerating, see? That is, I am supposing that the Time it would take an electron to physically accelerate across a particular portion of the gap between the electrodes is equivalent to the Space occupied by the barrier in a tunnel diode -- BOTH can be bypassed by Leaping/tunneling.   

       You may be assured that IF the electron makes a Leap, that WILL be accompanied by the emission of a photon. It is simply what Leaping electrons DO, inside voltage gradients (when they aren't absorbing photons instead, that is). As for the precise magnitude of the Leap, I slightly extend Einstein's logic, by which "Stimulated Emission of Radiation" was first described. Think of it this way: Two different photons may have different energies, but they still travel at the same speed. If they each collide with an electron, don't you think that the more-energetic photon is going to give its electron a bigger "punch"? So, if induced to Leap, it follows that that electron will make a bigger Leap than the electron hit by the wimpier photon. Well, the magnitude of an electron's Leap inside a voltage gradient is directly related to the magnitude of the photon that gets emitted during the Leap!   

       I admit I am ASSUMING that within a generic high-voltage field gradient, an electron that gets knocked by a two-electron-volt photon will Leap exactly enough to emit a new two-electron-volt photon. Inside a laser, this effect would be guaranteed whenever two electron volts happens to be the energy-level-gap between two possible electron-orbits. In the vacuum/free-electron environment, the actual Leap and emission may yield some other value X of photon-energy. However, because the voltage gradient is uniform, it follows that EVERY two-electron-volt photon that knocks an electron into making a Leap...will result in the emission of a photon of X amount of energy. That value of X can be adjusted, to match the incoming photons which we want to duplicate/"amplify", by adjusting the overall voltage between the electrodes.   

       [nomel], Bremsstrahlung is caused when an electron's path is forced to bend in a magnetic field (a curving motion at a constant speed nevertheless is defined as a type of acceleration, and whenever an electric charge experiences acceleration, a photon is emitted). No magnetic fields are involved here.
Vernon, Jun 10 2004


       I have not found anything that says this type of radiation has anything to do with a magnetic field, only that it can happen in a magnetic field due to the acceleration. I believe this is the method of photonic emmision you are speaking of.
nomel, Jul 02 2004

       Sorry to revisit an older topic but after I read the whole thing I just had to contribute ...   

       The device you are alluding to is similar to a Quantum Cascade Laser. QCLs are solid-state devices where (to make a long story short ... check the link I posted) light is amplified through a series of tunneling events and stimulated emissions. So essentially, electrons are traversing a finite distance through an electric field, tunneling across potential barriers, and generating a slew of coherent photons.   

       But let's clear up a few key points ...   

       An electron traversing a vacuum is, as mentioned, a free electron. A free electron in a electric potential gradient behaves like a ball rolling down a slope. Nothing impedes it from accelerating and so it just keeps on accelerating. Now suppose we put a wall on this slope ... on the quantum mechanical scale, this ball (electron) has a finite probability of tunneling through this wall (barrier). A simplified view is that indeed the ball leaps through the barrier (NOT OVER, but THROUGH). However, if there is NO barrier, than the electron has no reason to tunnel. There's nothing to tunnel through (it's free space). So essentially the electron just keeps accelerating. To the best of my knowledge, I have never heard of spontaneous tunneling through free space. Also important to note is the fact that the emission of a photon is not always the end result of tunneling. It just so happens that when an electron tunnels from a high energy state to a low energy state, nature dictates that the energy difference be conserved via a photon, phonon, etc. In the case of a vacuum, I suppose only a photon could be emitted. But to reiterate, free electrons will just get pushed by the electric field and probably would not spontaneously emit radiation.   

       So to the best of my knowledge, the physics you describe aren't exactly kosher ... but the idea is quite similar to the Quantum Cascade Laser. I'm no expert on laser physics and I'm not as up-to-date as I should be on the state of the art in this field, so I can't really tell you how far they've pushed QCLs since the 90s.   

       Just to give you some reference of the scales we are working with, the barriers in the QCLs are on the order of nanometers thick and the whole stack is typically on the order of tens of periods. Add it up and the device is on the order of a micron thick. I'm not sure how much they're biasing these devices but it's nowhere near the scale we've discussed here.
octal40, Mar 02 2007

       [octal40], thanks for the info. However, two points. Inside an atom, when an electron absorbs or emits an electron and does an associated quantum leap between orbits, it is effectively tunneling through free space.   

       Second, what voltage gradient is used in those Quantum Cascade Lasers? One crucial part of this Idea involves imitating the voltage gradient that exists inside an atom, specifically to create a condition in which electrons might do quantum leaps across free space. I completely agree that at ordinary voltages an electron is simply going to accelerate in ordinary Newtonian fashion.   

       But the half-baked notion here is that if the voltage gradient is high enough, then it will be "easier" for the electron to leap instead of to accelerate. We might say that its own inertia, teensy as it is, will start to be a factor in the result, when the voltage gradient is high enough. Nature does tend to take the easiest path to an end.   

       Oh, and remember that this electron isn't supposed to jump and emit a photon ONLY because of the gradient; there is the explicitly stated interaction of that electron with an incoming photon, inside that voltage gradient. In an excited atom the result is a second photon (and a now-unexcited atom). Here the electron at the "top" of the artificial voltage gradient is equivalent to being in that atom's excited state. The goal is to amplify existing light, not just to create light.   

       And, obviously, the notion still needs to be put to the test.
Vernon, Mar 02 2007

       I was writing a long long post but decided to whittle it down to one question:   

       Has anyone ever witnessed this stimulated tunneling/emission phenomenon in vacuum? The situation with the atom is different because there exist probability distributions for the different energy levels and there are regions where thye probability distribution is zero ... hence the tunneling. But in free space the probability distribution is flat or delocalized. If this was possible, my intuition tells me that it should have been witnessed already or at least well described theoretically in quantum mechanics textbooks.   

       Essentially, I think these are the main points in your idea: a) The goal is to convert as much potential energy into radiative energy. In essence, this would mean minimizing the amount of potential energy being turned into kinetic energy (i.e. acceleration). b) This can be achieved by tunneling into a state of equal energy (triggered by an external photon in this case) and then having the electron relax through radiative means. c) In essence the electron has travelled a finite distance through an electric field and converted the potential energy difference into radiative energy and NOT kinetic energy. d) However, tunneling, to the best of my knowledge, does not occur in the manner we would like it to in this case.   

       So here's an attempt at a half-baked modification of the idea ...   

       Suppose we could assemble a single row of quantum dots, each seperated by a few nanometers (within tunneling range), apply a giant field across the length of the chain, and then try to turn the thing into a quantum cascade laser EXCEPT using vacuum as the potential barrier. So essentially, it's basically your idea except with some means to allow tunneling through vacuum, or a vacuum quantum cascade laser. I suppose the question with this is why would we do this when we could just apply a huge field across a normal quantum cascade laser?? Maybe my idea is a little more like three-quarters-baked. At first glance, I cannot really see an advantage of doing this. :-P
octal40, Mar 02 2007

       [octal 40], so far as I know, this idea is completely original with me, such that nobody else has thought to look for stimulated tunneling/emission in the vacuum and those who COULD look haven't encountered this Idea yet. --Or at least haven't said anything about it. Regarding stuff in textbooks, there already is a lot about photon/electron interactions in free space --but none that I know of that also include a large voltage gradient.   

       Regarding your (a), (b), (c), and (d):
(a) exactly right.
(b) I don't quite understand your meaning. The simple way of talking about standard stimulated emission is to say that the passing photon "knocks" the electron in an excited atom to a lower energy state, causing the atom to emit its photon. It is required that the incoming photon match the energy of the naturally-emitted photon, for the second to be emitted in coherence with the first. Well, in free space and a high voltage gradient, any increment of distance across that space is equivalent to some photon's energy. So if this notion works at all, it should be less particular about the energy of the photon that knocks the electron (or "makes it tunnel") across some of that space.
(c) exactly right.
(d) Yes, tunnelling normally occurs where there exists some resistance to electron-motion. That's why I mentioned the word "inertia" in my last annotation. One of my biggest concerns about this Idea, if it works at all, is that we may have to totally flood the interaction zone with photons, to ensure that the electron DOES interact, and makes jump-after-jump across the vacuum between the electrodes. The net effect might NOT be a huge increase in the total energy of the already-passing-by light, simply because so many photons must already be passing through the region. On the other hand, it may be simpler to make a whole lot of this type of interaction site, than to make the sort of light-amplifiers that exist in the National Ignition Facility (see link).

       The problem with any sort of matter, be it quantum dots or atoms, in the path of the laser beam, is unwanted interactions between the laser beam and the matter. I like this Idea because that problem doesn't exist here.
Vernon, Mar 05 2007

       Without meaning to belittle the idea (which is very provoking [++]) - in the most simplistic terms are you proposing to shine a laser into lightning, and for want of a better term the "reaction" will convert the energy of the lightning into light?
sprogga, Mar 08 2007

       [sprogga], lightning doesn't have a high enough voltage gradient, and lightning doesn't work without an atmosphere to pass through.   

       This Idea involves a passage of electrons through a vacuum. (Heh, if it works, then maybe by using protons instead of electrons, and an even higher voltage gradient, we could copy a single gamma ray until we have a gamma-ray laser beam.)   

       We do want light to interact with those electrons passing through a vacuum. In one sense they SHOULD interact easily; electrons and photons do have a fairly high "interaction cross section". The actual interaction that takes place, however, may be different from that which is hypothesized here. To be determined!
Vernon, Mar 08 2007

       [Vernon], thanks for the reply!   

       OK fair enough, maybe nobody has looked for a phenomenon like this (I'm too lazy to comb through the journals at the moment), but ...   

       a) I still see no reason why the electron would tunnel. Tunneling is a quantum mechanical phenomenon and a free electron is not going to behave quantum mechanically. I don't see how applying a large voltage gradient is going to make a free electron in free space behave quantum mechanically. You mentioned something about inertia before ... maybe you can speak about that in detail. I think we need to avoid words like "easier" because it makes an argument without actually describing why/how something happens (you said it might be "easier" for it to tunnel ... etc). You agreed that the system would behave in a Newtonian fashion at low voltages ... what's the difference at high voltage? Electrons behave differently in atoms because of quantum confinement and we're speaking of free electrons here.   

       b) For arguments sake, I'll assume that this phenomenon can exist in the way you described (which I still am not convinced of). As you mentioned, photons can trigger stimulated emission events, making electrons tunnel down the gradient, lowering the energy of the electron. Note that a photon can also be absorbed and (if what you say is possible) tunnel backwards, increasing the electron energy? I don't know the statistics of these photon-electron interactions but both processes should occur.   

       c) As you had touched upon, without any feedback in this system, you would likely produce very little gain. To the best of my knowledge, optical gain devices need some sort of cavity (or a bragg stack, or something) to really get amplification. Maybe all that is required is a mirror and a partial mirror (like in lasers) ...   

       Again, I think the fundamental physics need to be addressed before discussing the logistics of how to do it.
octal40, Mar 08 2007

       [octal40], Regarding (a), you wrote: "Electrons behave differently in atoms because of quantum confinement and we're speaking of free electrons here." The thing is, while QM was devised to described how electrons behave in atoms, QM is not limited to that realm. This is why QM events can be found in all sorts of odd places, like particles interfering with themselves in free space and a couple of slits. I think I once read something to the effect that that superfluid helium can siphon itself out of a beaker, with no siphon actually needed. For some of the background information ("fundamental physics") out of which this Idea might become predictable, see "The Ghostly T.O.E." link.   

       I mentioned inertia because it essentially is "resistance to acceleration". Obviously a basically at-rest particle must accelerate before it can go anywhere, so an electron at the tip of an emitter needlepoint, under the influence of a high voltage gradient, will experience this resistance, at least a little, before actually starting across a gap. The difference between low and high voltage is the degree to which that resistance is a factor. Kind of like the difference between pushing on a tennis ball with your finger and swatting it with a racket; have you seen how much the thing deforms (in a high-speed photo) because of inertia?   

       Meanwhile, one of the reasons an electron tunnels through a solid barrier is because there exists resistance to motion through the barrier. Well, in theory the type of resistance is irrelevant; if ANY exists, then an electron has a probability of bypassing it by tunneling. As in "easier" (the path of least resistance.) Do note the detailed explanation/interpretation of ordinary tunneling in "The Ghostly T.O.E." Some of the key factors involved exist everywhere and all the time, including free space -- and some aspects of that existence will be enhanced by the high voltage gradient of this Idea.   

       Regarding (b), I do not disagree with that notion. However, I don't know why there should be equal probabilities involved, for the two events (absorption and stimulated emission). The existence of the high voltage gradient "primes" the electron for stimulated emission; it is more natural for it to go down-gradient than up-gradient. Well, an atom that absorbs a photon not only typically starts out at zero-excitedness (zero probability of emission), it also offers an evironment of semi-stability, for the higher-energy/excited state. Where is the equivalent of either of those factors in this description? OK, I know that there are lasers that work by using different frequencies of light, one for emitting and the rest for pumping atoms, but in this Idea only one frequency is chosen. Also, while in a single-frequency laser undesired absorptions exist, the reason this is undesired has more to do with the absorbed energy being converted to atomic motion (heat) than anything else, because otherwise the photon would eventually be re-emitted as part of the beam. That is NOT a factor here; any electron that Leaps up-gradient can also go down-gradient again, with no energy lost.   

       Regarding (c), the National Ignition Facility laser may have an initial reflective cavity, but once the pulse leaves, it goes through a number of pre-charged single-pass amplifiers. See link. This Idea is about a single-pass amplifier. A variation is mentioned in one of the early annotations; search this page for the word "razor".
Vernon, Mar 09 2007

       [Treon], maybe...but I have my doubts. It could very well be that in a magnetic-field gradient electrons can exhibit various quantum-increment properties, just as they exhibit such in the electric-field gradients around atomic nuclei. But likely there will be significant differences, since nuclear electric fields are "unipolar" and all magnetic fields are "bipolar".
Vernon, Jul 11 2007

       I think the electrons would resonate at the wave frequency of the coherent beam of photons which are passing through the path, but the DC offset of 40,000 volts through a vacuum resistance of 376 ohms (i.e. 106 amps DC) would render this effect negligeable, effectively scattering the photons in all directions (as soon as the position of the photon becomes certain via electron interaction, the coherent momentum of the wave pattern then becomes uncertain ~ <light scatters>).   

       Now if the voltage oscillated with an amplitude value of 40,000 volts and a frequency of about 503 THz (approx frequency of yellow/orange light) it would definantly work to amplify the laser beam until the needles become vaporized from the high energies of the oscillating electric field.   

       Of course, this would be using energy from an external source to amplify the overall energy flux of the laser (number of coherent photons/area) though, so energy in equals energy out, and it's just not as efficient as making the laser emitter bigger in the first place because of the inherent loss of energy due to heat from electron collisions (in the wires).
quantum_flux, Jul 12 2007

       //503 Hz (approx frequency of yellow/orange light)//
That's not even off the right hand side of a piano keyboard.
AbsintheWithoutLeave, Jul 12 2007

       Sorry, I meant to say 503 TeraHertz.... <error corrected>, also the phases would have to be in step too or else there could be laser light cancelation in the direction of the laser beam.
quantum_flux, Jul 12 2007

       [quantum flux], you can generate light directly by making electrons oscillate at 503THz. But electrons inside atoms, moving down from the excited state to the ground state, don't oscillate. The photons they emit are the result of the quantum leaps they make. THAT's the effect I want to imitate, with this Idea.
Vernon, Jul 12 2007

       the amount of energy lost or gained in a quantum leap is equivalent to heisenburg's constant times the angular frequency of the photon that is emitted.... E=hw.... and "w" for a photon is eqaul to 2*pi times the wave frequency of the photon.... E=h*(2*pi*f).
quantum_flux, Jul 12 2007

       //Sorry, I meant to say 503 Terrahertz//
"TeraHertz", spelling corrected.
AbsintheWithoutLeave, Jul 12 2007

       I am adding Vernon to my list of books to read.
MaxwellBuchanan, Jul 12 2007


back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle