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Originally Posted by lwcamp
Modern x-ray lasers are mostly generated by particle beams, so if you don't have the minimum size for the particle beam you don't get the laser.
We don't have gamma ray lasers, but you can use particle beams to get narrow gamma ray beams using laser Compton backscatter (in principle, you can also use positron annihilation in flight, but that's a tech path that we are not currently pursuing in favor of Compton backscatter).
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How likely is it that the size of particle accelerator you'd need for a particle beam weapon is significantly larger/smaller than the one you'd need for an x-ray laser weapon? Similarly, am I correct that the accelerator for a graser would likely need to be orders of magnitude larger than the one for an x-ray laser? Does Compton backscatter present its own issues with miniaturization? How does positron annihilation in flight lead to a coherent beam?
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How could it work? You accelerate up a bunch of electrons and send it through the gap between two Halbach arrays of magnets (a "wiggler").
https://en.wikipedia.org/wiki/Halbach_array
This forces the electrons to move in a sinusoidal pattern. The modes of the electromagnetic field whose force is constantly opposing the motion of the electrons will have work done on them and be amplified. With a suitably long wiggler or a resonant cavity, you can get a very narrow band of modes, like a laser beam. If the radiation field is intense enough and the wiggler is long enough, the electrons will self-organize into bunches to produce super-radiant coherent motion. Now you have a free electron laser.
For a tuneable FEL, you will need separate wigglers for different frequency bands. The wiggler for the x-rays will have a pitch way too short for when you need visible light, so you would divert the electron bunches to a visible light wiggler. (The visible light wiggler would probably also be inside a Fabry-Perot resonant cavity,
https://en.wikipedia.org/wiki/Fabry%...interferometer
allowing you to achieve your laser behavior threshold with a much shorter wiggler.)
Luke
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So TLDR; if you want to justify a non-tunable x-ray laser you could assume the multiple wigglers was not worth the trouble?