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Electron free lasers

  1. Jul 27, 2010 #1
    I must say that after reading about this concept over the last few days it is one of the most fascinating things. Specificaly the concept of self amplification of spontaneous emission.(SASE)
    I am wondering is it possible to use a coventional synchronotron as an EFL? Apart from the undulator what else would need to be changed.Because in both cases the electrons need to acquire a relativistic speed.
    Or does the EFL need to be built from scratch.
    Also is it a pre condition that in an EFL the path of the elctrons is curved,i mean because the radiation is emmited as they pass over the undulator, so i am thinking it should not make a difference.

    If anyone understands an EFL a lot, i think its pretty cool and would like some feedback.
  2. jcsd
  3. Jul 27, 2010 #2
    I'm not an expert, but here's what I know:

    A synchrotron can't be converted into an FEL, the two are fundamentally different. The path of the electron beam (ignoring the oscillations in the plane as it passes through the undulator) needs to be straight. That's why you can turn a linear accelerator into an FEL, but not a synchrotron. Key to the operation of an FEL is the fact that the radiated field of the electron beam remains in phase with the electrons, and acts back on it. In a synchrotron, the beam is moving along a curve so the radiated field propagates away and does not act on the electron beam.
  4. Jul 28, 2010 #3


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    Laser must have at least 2 possible excited states to operate. The lower of the two must be metastable with respect to the higher state. That's the only way you can build up an inverted population, which is a requirement for lasing.

    If you can explain to me how to create a metastable excited state in a synchrotron, we can discuss possibility of using that state to build a laser.
  5. Jul 28, 2010 #4
    Maybe you know something I don't, but I really don't think this is right. There is no lasing medium for an FEL, the name itself implies that the electrons are free, so how can they have different energy states? It's simply their trajectory that causes the emitted radiation to be coherent. There is no transition between energy levels.
  6. Jul 28, 2010 #5


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    Here's a good link as an intro to SASE FEL


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