EFL: Electron-Free Lasers & Synchrotrons

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Discussion Overview

The discussion revolves around the feasibility of using a conventional synchrotron as an Electron-Free Laser (EFL), particularly focusing on the concept of self-amplification of spontaneous emission (SASE). Participants explore the necessary changes to a synchrotron to facilitate this and the implications of electron trajectories in relation to radiation emission.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses fascination with SASE and questions whether a conventional synchrotron can be adapted into an EFL, asking about necessary modifications beyond the undulator.
  • Another participant argues that a synchrotron cannot be converted into an EFL due to fundamental differences, emphasizing that the electron beam must travel in a straight path for an EFL to function properly.
  • A participant discusses the requirement of metastable excited states for lasing and challenges the idea of creating such states in a synchrotron, suggesting that an FEL does not have a lasing medium and relies on the coherence of emitted radiation from the electron trajectory.
  • One participant reiterates the need for metastable states and questions how they could be established in a synchrotron, indicating a lack of clarity on the relationship between energy states and the operation of an FEL.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the possibility of converting a synchrotron into an EFL, with some asserting it is not feasible while others explore the theoretical implications of doing so. The discussion remains unresolved with competing views on the requirements for lasing and the nature of electron states in this context.

Contextual Notes

Participants express uncertainty about the necessary conditions for lasing in relation to electron states and the structural requirements of synchrotrons versus EFLs. There is a lack of consensus on the implications of electron trajectories and the role of metastable states.

oddiseas
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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.
 
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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.
 
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.
 
K^2 said:
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.

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.
 
oddiseas said:
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.

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

http://hasylab.desy.de/facilities/s...rotron_radiation_to_a_sase_fel/index_eng.html

Zz.
 

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