Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Polarization of an emitted photon

  1. Dec 27, 2014 #1


    User Avatar
    Gold Member

    Bonnes fetes de Noel.

    When an excited electron returns to its ground state a photon is emitted.
    Suppose that the electron's spin skip from +1/2 to -1/2 (around z)and that the photon has a momentum parallel to z.
    I suppose that this photon has a circular polarization around z (Is it true?)
    The problem is that there is no spin alone conservation but total angular momentum conservation.
    Knowing all about |e> and |g> what can we calculate about the polarization of the emitted photon?
    Have you links?
    Last edited: Dec 27, 2014
  2. jcsd
  3. Dec 27, 2014 #2


    User Avatar

    Staff: Mentor

    Merci !

    To first order, the spin of the electron is not coupled to the electromagnetic field, so spin-flip doesn't occur during transtions. Look up selection rules.

    You need to consider the total angular momentum of the electron, ##j##. For an emission in which you have ##j = +1/2 \rightarrow j' = -1/2##, that would correspond to a ##\sigma^+## photon, which means that if the photon is travelling along z, it has right-handed circular polarization. A recent discussion on this subject can be found here.
  4. Dec 27, 2014 #3


    User Avatar
    Science Advisor

    You should also take in mind that a photon in a momentum eigenstate is not in an eigenstate of photon angular momentum, which are the vector spherical harmonics.
  5. Dec 28, 2014 #4


    User Avatar
    Gold Member

    Thank you
    i read the links and questions will follow.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook