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Radiation from electron oscillations at plasma frequency?

  1. Jul 7, 2011 #1
    Hi, there have been a number of recent papers with regards to radiation from hypervelocity meteor impact, where the authors propose that the radiation originates from self-consistent electron oscillations at the plasma frequency. Some examples:

    1) Close et al - Journal of Geophysical Research, 115, A12328 (2010)
    http://www.agu.org/pubs/crossref/2010/2010JA015921.shtml (apologies if you don't have access)
    Related poster:
    http://aa.stanford.edu/students/media/posters2011/Alex_Fletcher.pdf [Broken]

    2) Foschini - Europhysics Letters, 43, 226 (1998)

    In these papers, what I understand is that they basically consider electron oscillations at plasma frequency, take each oscillating electron as a radiating dipole, and integrate the radiated power over the entire finite plasma.

    But are these mechanisms correct? I thought these plasma oscillations are nonradiative, because the displacement current cancels the electron current so that there is no magnetic field involved. (I am assuming no nonlinear effects here, which the authors do not consider anyway.) If the radiated electromagnetic field strength (rather than power) is integrated over the finite plasma, I am expecting that the radiated field strengths will destructively interfere so that there is no radiation.

    Also, note that I do not think the authors are referring to other finite-plasma oscillation modes that are indeed coupled to electromagnetic waves outside the plasma, because these modes are not at plasma frequency, and also because these modes cannot be derived self-consistently solely based on the restoring force from charge density generated by the electron motions, which the authors seem to have alluded to.

    There seems to be a somewhat similar controversy when some authors proposed a mechanism for the observation of terahertz radiation from femtosecond laser filaments, again based on radiation from these plasma oscillations (apologises if you don't have access):
    Cheng, Wright, Moloney - Physical Review Letters, 87, 213001 (2001)

    which generated some arguments and counterarguments:
    Shvets, Kaganovich, Startsev - Physical Review Letters, 89, 139301 (2002)
    Cheng, Wright, Moloney - Physical Review Letters, 89, 139302 (2002)
    Tikhonchuk - Physical Review Letters, 89, 209301 (2002)
    Sprangle et al - Physical Review E, 69, 066415 (2004)

    In summary, I believe that the proposed mechanisms of radiation from electron oscillations at plasma frequency are wrong, but being a beginning researcher, I'm not particularly confident and so would like to hear the viewpoints on my counterarguments from more experienced members of the forum. Thanks!
    Last edited by a moderator: May 5, 2017
  2. jcsd
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