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Electric and Magnetic fields of light

  1. Aug 27, 2009 #1
    It is my understanding that for all of spectrum of light Electric and Magnetic fields have the same phase.
    And both fields have correlation - Magnetic fields amplitude grows along with Electric one.
    I am wandering - is it possible to generate light with phase shift between fields ?
  2. jcsd
  3. Aug 27, 2009 #2


    Staff: Mentor

    It is certainly possible to generate electric and magnetic fields that are out of phase, but they wouldn't radiate as a source-free wave in vacuum, so I wouldn't call it "light".
  4. Aug 27, 2009 #3
    thank you for your response.
    If i may to elaborate the debate. Is it possible to create a phase variation in a beam of light. Say, we have a laser and with help of some instruments to change the phase between the fields of that laser ?
  5. Aug 27, 2009 #4


    Staff: Mentor

    Not in vacuum.
  6. Aug 27, 2009 #5
    If you propagate light through a lossy material (i.e. absorption occurs), then, in general, the electric and magnetic fields will be out of phase.
  7. Aug 28, 2009 #6


    User Avatar
    Science Advisor
    Gold Member

    I don't see that happening. I agree with DaleSpam (mmmm... spam) and I cannot think of a situation off-hand in a source-free region where you get a propagating wave where you can get either a temporal or spatial shift in the phase in one field over the other. The time-harmonic solution to Maxwell's equations dictates that the electric and magnetic fields must have no temporal phase shift, but the separation of variables that you get with the time-harmonic case means that the time-dependence is independent of the medium that the wave is propagating in, unless the medium itself is changing over time. Then the spatial phase dependence between the electric and magnetic fields is also the same. The magnetic field is related to the curl of the electric field, the attenuation in the electric field will have the same effect on the magnetic field. You can introduce phase shifts to the wave as it propagates, but these phase shifts are applied to both the electric and magnetic fields.
  8. Aug 28, 2009 #7

    For harmonic waves (time and space), B is proportional to kxE. In lossy media, k is complex. Therefore, B has an additional phase factor with respect to E.
  9. Aug 30, 2009 #8
    cmos, thank you for your reply.
    With respect to propogating light through a lossy media. What would happen once beam of light is out of lossy media ? Would the phase variation return to zero or will it remain ?
  10. Aug 30, 2009 #9
    By the same argument, if you propagate back out into a lossless medium, then the electric and magnetic fields should be back in phase with each other.
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