1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Free Electron Laser

  1. Sep 10, 2014 #1
    1. The problem statement, all variables and given/known data
    i1k9vm.jpg


    2. Relevant equations
    2. (b)

    I didn't understand how can I find the app. wavelength


    3. The attempt at a solution

    I tried : the electron move over λu with velocity β so the wavelength is λ≈λu
    but its not the right answer.

    my lecturer told me I should consider also the dopler

    I only know that the answer is :
    λ≈λu /(2*γ2)

    γ= gamma
    THANK YOU!
     

    Attached Files:

  2. jcsd
  3. Sep 11, 2014 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    This is the distance the light can travel while the electrons move by 1 structure length - but then the electrons moved forwards as well. What is the difference between those two distances?
     
  4. Sep 11, 2014 #3
    the electron moves λu while the light moves λ≈λu /β
    so the difference is λu [1/β-1]

    so how can I use this fact to find the wave length?

    I tried use the approximation β≈1-1q/(2*γ^2) for ultra-relativistic electrons
    but still didnt get the right answer....


    thank you
     
  5. Sep 11, 2014 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    1/β is also 1/(1+β-1) where β-1 is small, so you can express that fraction as ~1-β+1
    That should lead to the right answer.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Free Electron Laser
  1. Free Electron Laser (Replies: 0)

  2. Free electron metal (Replies: 1)

Loading...