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Thread: Free Electron Laser

  1. #1
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    Default Free Electron Laser


  2. #2
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    Cool Impressive!

    They are almost there... I wonder If there is a *really small* FEL constructed ever, I was really appealing the way of FEL works from the point of view of theoric *simplicity*: you took a bunch of electrons, kick them up to a speed, and then make them swing on a magnetic field.
    It's a pitty when one goes for the figures and discovers it is far far beyond the possibilities of a *well-funded garage laboratory*... At least, this was the bottom line last time I readed about it, but... has something changed on this last years?
    Do have -in any way- the modern technologies made it possible to be nearer to put a small FEL on your garage?
    I guess nothing has changed, at the end, you're working with smallest pieces of matter, and I guess this *ALWAYS* means huge amounts of power as to, simply, get them where you want them to be and be as accurate as it is needed to be.
    I guess that's the best of having a lasing medium: the electrons are there, they are mostly fixed and predictable, and so the "harnessing" and "creation" energy for the electrons is provided by the matter of the lasing medium. The worse is thar they are too much fixed and a new material is needed for almost each wavelenght, and no every wavelength is possible, not at least before a *new* material is discovered for that precisse wavelenght.
    Perhaps in the middle future nanotechnology and nanostructured materials could reach to a point in which you can have a lasing medium with "elastic" or "commutable" lasing levels, and so one could have a universal-wavelenght lasing medium... Who knows! It could be possible from the "shallow" or "conversational" point of view... Physics (always) has to peak!

    Well, sorry, a bit of mind speaking after reading the good article and site you shown in the post... Thank you!

    Cheers

    NOTE editing: I hope it is more readable now. Anyway, not important or "well funded" things said here, just conversational...
    Perhaps someone out there can add severe and documented commentaries, they will be welcomed (understanding the first poster, hivelaser, is agreeing, of course!).
    Thanks for reading.
    Last edited by Mel; 07-10-2011 at 06:37. Reason: Better styled

  3. #3
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    Default

    If you break up your Brock of text with a few paragraphs...perhaps more
    members would read it...
    I gave up after the 2nd line....

    Jerry
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  4. #4
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    Talking Agreed...

    Quote Originally Posted by lasersbee View Post
    If you break up your Brock of text with a few paragraphs...perhaps more
    members would read it...
    I gave up after the 2nd line....

    Jerry
    Touché! Yeah, I'll have to be carefull with the style... I beg pardon, I'm a beginner at the forums... And probably I
    posted it before looking at a post-preview...
    But I absolutely agree with you, myself, I've barely reached the third line when re-readed now!
    Could it be edited? Anyway, perhaps it's not so interesting to do it (but still I'd like it to be more readable!)

    Cheers, and thanks :-)

  5. #5
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    I think you're missing the point of a FEL.

    http://en.wikipedia.org/wiki/Free_electron_laser

    Basically, a FEL (free electron laser) is a magnetron tube (the kind you find in a microwave oven) stretched out flat. It works on the same principle.

    On one end, electrons get injected from a cathode and they travel through a vacuum (not an actual lasing medium) until they reach the other end. During their travel in the tube, they encounter a magnetic field which is at right angles to the tube (e.g. pointing straight down) causing the electrons to sway back and forth due to the Lorentz force.

    The photon emission comes from the change of speed and direction the electrons encounter in their path (synchrotron radiation) and this is what determines the laser's wavelength. It depends on the electron speed (tube voltage) as well as the magnetic field strength, whereas the laser's power will vary with the amount of electrons passing through it each second (tube current).

    Most of the basic components in a FEL can be found in household items -- the electron accelerator used, for example, is similar to a CRT 'electron gun', and the wiggler magnets can be compared to the ones found in a microwave tube. The challenge is to put it all together properly and safely -- one of the reasons FELs are so big is not because they need to be for adequate lasing, but because the support hardware required (vacuum system, electron accelerator, etc.) will work a lot more efficiently at higher powers and larger sizes.

    I would personally like to see a bench-top, visible light FEL in action, but I'm not sure whether that's even possible.

  6. #6
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    For one, the vacuum pump needed can't be found in my household.

    A guy at FELIX told me that it's not considered to be a laser in its strict sense by most physicists.
    But a FEL creates a powerfull coherent monochromatic beam, so why bother.

  7. #7
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    I think you're missing the point of a FEL
    I'm not missing it, I hope! :-)
    My point was simply: I'm pretty sure you cannot make a synchro-cyclotron or similar (as a base for a FEL) as small as you want, in a similar way an aeroplane needs a minimum runway to land/take-off.
    Electrons need to be "injected" with enough energy, and that's related to the radius of the machine, and also, as you said, by a big magnetic field. As you stated, all this stuff needs to be cooled, and also a "free-of-matter path" must be provided for the electrons along its way, so again one needs energy to make really high vaccuum. Finally, ligth is "harvested" using wigglers, and so an amount of energy is used again to make electrons "dance". I agree with the "larger implies more efficient" principle, but still, the size of a FEL will be BIG no mattering the final power, as there are constraints by design/principle. The bottom line would be "free electrons = lots of energy and plenty of space to harness them".

    For one, the vacuum pump needed can't be found in my household.
    A guy at FELIX told me that it's not considered to be a laser in its strict sense by most physicists.
    But a FEL creates a powerfull coherent monochromatic beam, so why bother.
    Yeah -bart-, you wont either find any of the magnets or the superconductive "wires"...

    From theory, in a "traditional" LASER, one cannot (mathematically) distinguish between both fields, ie, the main laser output and the field on the resonator that causes the stimulated emission. In FELS the output is not "so coupled" to the original field, indeed, there is spatial but no temporal coherence due to the "bunching" that wigglers apply to electrons.
    In the other hand, the physics principle is different: light emission between energy states of an electron in matter vs. syncroton radiation.

    Cheers!

  8. #8
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    Quote Originally Posted by Stoney3K View Post
    I think you're missing the point of a FEL.

    http://en.wikipedia.org/wiki/Free_electron_laser

    Basically, a FEL (free electron laser) is a magnetron tube (the kind you find in a microwave oven) stretched out flat.
    It's kinda similar but it actually works on a different principle. In a magnetron most of the radiation actually comes from electrons resonating in drilled metal cavities around the electron beam; in a free electron laser the radiation comes from the beam itself. It's a bit like the difference between, say, a slide trombone, which has a linear topology, versus a panflute. In a panflute, a jet of air causes a vibration in a column of air that is closed at one end, which produces the sound; in a trombone, the sound is produced directly by the air resonating in its direction of travel.

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