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Linas

Sun Mar 27 2011, 06:45PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

How hard is to make FEL for visible light at least 1mW CW ?
well, i can get electrons and accelerate to high speed like in CRT, then squeeze to dense beam with coil, and then pass through 1m undulator made from ring shape neodymium magnets N45 or higher grade (lot of them, 15.000gaus each)

Dr. ISOTOP

Mon Mar 28 2011, 12:06AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Nearly impossible.
You'll need lots and lots of high vacuum stuff.
It'll be like building a fusor, only harder.
Why do you need a FEL? Just for fun, or for work?

Meatball

Mon Mar 28 2011, 05:03AM

Registered Member #2401 Joined: Mon Sept 28 2009, 04:25PM
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Posts: 74

What CAN'T you do with an FEL? You have the freedom of virtually whatever wavelength you want. But, I agree that it is extremely daunting even for an a tinkering pro.

I was under the impression that they are still in the development stage if you will. They haven't yet been perfected, and they still cost loads of money for a research facility to setup and run.

Linas

Mon Mar 28 2011, 06:08AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

bwang wrote ...

Nearly impossible.
You'll need lots and lots of high vacuum stuff.
It'll be like building a fusor, only harder.
Why do you need a FEL? Just for fun, or for work?

I am searching activities for summer.
in my university should be some good vacuum pump

Zero

Wed Mar 30 2011, 04:16PM

Registered Member #3588 Joined: Sat Jan 08 2011, 11:19AM
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I would be happy with a small gasdynamic Co2 laser...anyone? :)

Marko

Fri Apr 01 2011, 07:22AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys,

For me, operation of free electron lasers till this day has been a wall-banger. It's at first hard to imagine it can be called a laser at all without any atoms that can be stimulated in order to get stimulated emission, and operation at first seems more like of a magnetron than a laser. But if you add mirrors to it they will indeed increase gain proving it's truly a laser, and electrons seem to have their photon releases influenced with other photons, and this happens without mirrors as well.
It's hard to imagine these discrete quantum mechanical effects from coming from electrons that are wiggled by macroscopic magnets. Perhaps understanding it one day might help understanding optical lasers better.

Despite the concept of a FEL looks simple, the experimental ones look like rather large and costly machines. I don't know whether your idea would work at all, and what are all the catches for this kind of laser, but some general advice I could think off is:

- I wouldn't bother making the electron optics myself, I'd try to get one from an oscilloscope, a TV, or something like an electron microscope if luck is high enough. You can just put it into your vacuum vessel.

- Experimental lasers seem to use very high electron energies, in ranges of tens of MeV. For a practical homemade linear accelerator, you'll probably be limited to under 1MeV and I'm not sure whether this laser is plausible with such low energies. This would still be a challenging voltage to produce and a major X-ray hazard as well requiring lots of shielding. As far as I recall, wavelength is dependent on distance between magnets divided by lorentz factor, or perhaps squared lorentz factor.

- Experimental lasers seem to use massive iron cored electromagnets, although I don't see why wouldn't Nd magnets beat them. They are only slightly weaker and can be compactly integrated into vacuum vessel, and produce no heat as well.

- If you produce a beam you'll need to figure out how to get it out of the vacuum tube, a Brewster or antireflection coated window required.

Marko

cedric

Tue Apr 05 2011, 12:51PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

I always wonder if it was possible as well,that would be a crazy ,I think like Marco that the accelerating voltage have to be really high to reach a point where cyclotron radiation occur in the visible spectrum,in theory it is possible to create very high voltage (megavolt range) using piezoelectric ceramic bar few meter long ,immersed in oil running through a thermal cycle,that could be a start ,it's hard to find technical information on the subject on the web but those machine always have the size of a small building...

Linas

Tue Apr 05 2011, 04:13PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

just talked with lecture from university, he said that "only" problem is very high vacuum, 1e-10mmHg. so turbo-molecular vacuum pump is needed.
and it have to work all the time.
it's quite simple to get beam of laser,but it can be far IR.
and power should be quite good

Pinky's Brain

Thu Apr 07 2011, 08:09PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Marko wrote ...

It's hard to imagine these discrete quantum mechanical effects from coming from electrons that are wiggled by macroscopic magnets. Perhaps understanding it one day might help understanding optical lasers better.

Do we need quantum mechanics to model FEL? Can't we take the macroscopic view and just use Maxwell equations? I suspect that an ordinary antenna has much in common with a FEL.

Meatball

Tue Apr 19 2011, 03:48AM

Registered Member #2401 Joined: Mon Sept 28 2009, 04:25PM
Location:
Posts: 74

Understanding an FEL won't help your understanding of ordinary gas medium lasers for sure. :)

Quantum Mechanics is needed to predict exactly what wavelength you will output and at what energies the electrons will need to be accelerated at.

I've seen where they are accelerated through a potential of about 90kV.

Not impossible at all. But I think the custom glass pieces, vacuum pumps, and perfectly shaped magnets of large sizes will be some of the first things to get in the way. You might as well put out a bid for the job.

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