What's a Free Electron Laser

[INRM]

What's a Free-Electron Laser?

INRM

[AgeGap]

Never heard of it (http://en.wikipedia.org/wiki/Free-electron_laser). Also New Scientist here. (http://technology.newscientist.com/article/mg18925351.300.html;jsessionid=55B472E043C39093A59 459E4D97B1546?DCMP=ILC-OpenHouse&nsref=mg18925351.300INT)
Sounds cool though. On the one hand a death ray and on the other a way to look at the smallest building blocks of life, giving us the information required to develop new medicines.

[Timothy]

When looking for basic information, a quick Google or Wikipedia search is a far more effective way of getting a lot of material, rather than asking members to type it in themselves. What's a Free-Electron Laser?

INRM

[AgeGap]

When looking for basic information, a quick Google or Wikipedia search is a far more effective way of getting a lot of material, rather than asking members to type it in themselves.
A fair point but then I would have never heard of a free electron laser. Gotta love wikipedia though. It usually has some good links as well.

[Vorticity]

I used to work at the FEL facility at UCSB in the late 90's.

http://sbfel3.ucsb.edu/

I was going to explain what an FEL is myself, but wikipedia saves me the typing:

To create a FEL, a beam of electrons is accelerated to relativistic speeds. The beam passes through an FEL oscillator in the form of a periodic, transverse magnetic field, produced by arranging magnets with alternating poles within a laser cavity along the beam path. This array of magnets is sometimes called an undulator, or a "wiggler", because it forces the electrons in the beam to assume a sinusoidal path. The acceleration of the electrons along this path results in the release of a photon (synchrotron radiation). Since the electron motion is in phase with the field of the light already emitted, the fields add together (coherently) and since light intensity is dependant upon the square of the field the light intensity is increased. Instabilities in the electron beam, which result from the interactions of the oscillations of electrons in the undulators and the radiation they emit, leads to a bunching of the electrons which continue to radiate in phase with each other in contrast to conventional undulators where the electrons radiate independently.[2] The wavelength of the light emitted can be readily tuned by adjusting the energy of the electron beam or the magnetic field strength of the undulators.

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

[Vorticity]

Incidentally: It was dangerous to be in the same room as the wiggler while it was in operation. The amount of incidental radiation was beyond the recommended limits. So the room had to be vacated when the laser was on. The light from the laser was channelled via mirrors through holes in the wall to the lab next door, where the actual experiments were performed.

I had a summer research job there developing low-pass filters. (It didn't work.)

[Cuddles]

Incidentally: It was dangerous to be in the same room as the wiggler while it was in operation. The amount of incidental radiation was beyond the recommended limits. So the room had to be vacated when the laser was on.

Well yes. Standing inside particle accelerators is generally considered not very sensible.

I have to nipick the Wiki article though. Undulators and wigglers are not the same thing. Wigglers have a high (>>1) strength parameter, and give very large photon flux across a wide spectrum. Undulators have a low strength parameter (usually <1) which means the electrons follow a sinusoidal path. This results in coherent radiation, giving a very high flux in a narrow bandwidth, but relatively little at other wavelengths. FELs use undulators, not wigglers, because the whole point is to get coherent radiation.

[Ziggurat]

The Stanford Linear Accelerator Center (SLAC) is in the process of creating the world's first X-ray laser (http://www-ssrl.slac.stanford.edu/lcls/index.html) using their linear accelerator. It's expected to come online in 2009, and will be wicked cool when it does.

[Soapy Sam]

I thought they were one-shot objects, pumped by a nuke.

It's not bloody quantum, is it?

[Ziggurat]

I thought they were one-shot objects, pumped by a nuke.

Nope.

It's not bloody quantum, is it?

Every laser is quantum. Lasing is a quantum phenomenon.

[ponderingturtle]

I thought they were one-shot objects, pumped by a nuke.

No it is just that was a suggested way of creating them for use as a weapon. They came from Teller's idea of the only way to get a laser that would be an effective weapon into space.

I can't seem to find any postive tests of his proposed system.