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Can a photon be deflected?

  1. Jun 10, 2015 #1
    From my understanding, photons travel at the speed of c in the straightest line possible. Say I take a photon and send it off to the right toward a mirror. It hits the mirror and is deflected in the opposite direction in relation to the angle of incidence.

    My question is is the photon that is deflected to the left the same photon that I initially sent right? Or did some annihilation/re-creation event happen at the mirrored surface to create a similar but uniquely distinct photon now traveling in the opposite direction?

    More generally, once a photon is set going, say either to the left or the right in an arbitrarily defined coordinate system, is it's existence confined to a straight line in that direction?
     
  2. jcsd
  3. Jun 10, 2015 #2

    Nugatory

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    Both speed and direction of travel are defined in terms of position and changes in position - and a photon doesn't have a clearly defined position except when it is actually interacting with something. Thus, there is no sensible way of talking about photons travelling in straight lines at the speed of light - bursts of electromagnetic radiation behave that way classically, but photons are not little bits of electromanetic radiation and they cannot be described classically. We can't answer a question about a photon that is deflected is the when the entire concept of deflection is classical and depends on concepts like direction and speed of travel.

    You'll see Feynmann's "QED: The strange theory of light and matter" recommended here from time to time. If you haven't had a chance to give it a try, you should. Photons just aren't what you think they are.
     
  4. Jun 10, 2015 #3

    tech99

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    When the photon hits the mirror, it causes electrons to move and absorb energy. They then re-radiate the energy in a new direction. As far as I can see, and I am often wrong, in order to influence an EM wave in any way, whether reflection, refraction, diffraction or absorption, you need either an electric charge, such as an electron, or a very light and moveable magnetic pole.
     
  5. Jun 10, 2015 #4
    Ok, let me extend the question..Let's take a massive object such as an electron. Can we say that the deflected electron is the same electron once it interacts with an object and get's deflected in the opposite direction?

    More specifically, is there a qualitative difference in how this interaction unfolds for a photon versus an electron?
     
  6. Jun 10, 2015 #5

    Nugatory

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    Classically, yes. Quantum mechanically, no.

    Only in that classical descriptions of electron interactions are often useful as excellent approximations, whereas there is no such thing as a sensible classical description of photon interactions.
     
  7. Jun 10, 2015 #6

    ZapperZ

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    Isn't this a rather strange question, considering that we have so many electron accelerators all over the world that do nothing but manipulate the trajectory of electrons?

    Zz.
     
  8. Jun 10, 2015 #7
    Again, from my understanding, these electron accelerators manipulate these trajectories in a rectilinear or curvilinear path. My question is specifically about the deflection of an electron (and photon) off of a reflective surface and what that abrupt change in direction implicates.

    More simply, I'm not talking about a hard smashing of an electron, rather a soft deflection.
     
  9. Jun 10, 2015 #8

    ZapperZ

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    The phenomenon of electron "bouncing" off the surface is a lot more complicated than with photons. First, there is no guarantee that you get the same angle of "reflection", unlike light bouncing off a mirror. This all depends on the nature of the surface. Secondly, depending on the energy, you could easily get secondary emission (look at the spectrum of secondary electrons versus primary electrons). Etc.. etc. Unless you have a specific scenario in mind (i.e. incoming energy, nature of the surface, etc.), then you can get a zoo of phenomena as the possible outcome.

    Zz.
     
  10. Jun 11, 2015 #9
    In quantum mechanics, identical particles cannot be distinguished. There isn't a true difference between an electron being absorbed and another emitted, and an electron which is scattered.
     
  11. Jun 12, 2015 #10

    f95toli

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    You can make electrons bounce of voltage potentials. There is a whole sub-field of electron quantum optics where people do e.g. H-B&T experiments and other correlation measurements. The source of electrons in this case is usually some sort of single electron pump (made from say GaAs) which "fires" very hot electrons (meaning their energies are way above the Fermi sea) on demand.
    By using gates you can then set up voltage barriers that can be used to manipulate the trajectory of the individual electrons, including making them bounce (and by carefully adjusting the barrier height you can also create a situation where 50% of the electrons are deflected and the rest are transmitted). By playing with the timing you can also transmit every second one etc.
     
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