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What does it mean for a plasmon to confine or guide light?

  1. Jan 27, 2012 #1
    I'm trying to grasp the basic concepts of plasmons and can't quite picture what is going on.

    When light is incident on small metal nanoparticles, it causes the conduction electrons of the metal to oscillate at the frequency of the photon. Is that a plasmon? Is that also the same as it being referred to a plasmon coupled with a photon (plasmon polariton)? Does one photon generate one plasmon?

    A few articles I read state that plasmons can pave the way to subwavelength optics. What does this mean and why is it a big deal?

    What does it mean to confine the light and why is that important? I can see how light propagation would be important, especially in something like data transmission, but how would plasmons play a role?

    I greatly appreciate any insight that can be shared!

  2. jcsd
  3. Jan 29, 2012 #2
    This is the basic idea, however the plasmon frequency is not exactly the photon frequency. The first thing that needs to be understood is that there are two different types of plasmons. First, there are oscillations of the bulk conduction electrons. these occur at the plasma frequency and are not excited by light, but can be excited by fast electrons.

    The second type of plasmons that are encountered are usually some form of surface plasmon. If these are excited by fast electrons then they are simply known as surface plasmons. However, if you can meet the correct boundary conditions light can couple into a surface plasmon. This create what is know as a surface plasmon polariton. However, this coupling requires the phonton to gain momentum somehow for the coupling process to occur since the surface plasmon curve lies to the right of the light line.

    The reasons that plasmons are an exiting way to use light for opto-electronsics is that the wavelength of a plasmon is much smaller and they have a relatively long propagation distance on the surface of a metal. Also realise that if you do not confine the light/plasmon then it will just go every and not necessarily in the direction that you want. This was you could excite a signal with an optical wave packet and then have it perform some time of operation at the same scale as a microprocessor in a computer, and then when the operation completes it could out couple as a new optical signal. so you get the speed of light computing, with the compactness of current semiconductor technology. (sorry if this is not totally clear as I could probably due with one or two more coffee's this sunday morning.)

    Some good references to dig into this further would be:

    1) S. Maier - Plasmonics: Fundamentals and Applications (especially the intro through ch3 or so)
    2) I really like this review article by C. Genet and T. W. Ebbesen, Nature 4, 39 (2007).
    3) This is a more in depth one gong beyond the very basics A. V. Zayats, I. Smolyaninov, and A. A. Maradudin, Physics Reports-Review Section of Physics Letters 408, 131 (2005)
    4) for wave guiding concepts I would also check out the N. Engheta discussion piece in the Sept 2010 of Physics World

    There are more refs that I would give you but this will get you started.
    Last edited: Jan 29, 2012
  4. Jan 30, 2012 #3
    Hello Josh,

    good answer. I have a doubt too: when an EM wave is incident on an antenna electrons are set into motion and a current is formed. I know that has nothing to do with plasmons, correct?
    But why? Isn't a current motion of the electron cloud?

  5. Feb 8, 2012 #4
    Well I am not really an expert in antenna theory and it has been a good number of years since I even had the basics. But if I remember correctly the operation of an antenna does not rely on the collective oscillations of the metal plasma. Plasmon related phenomena are collective excitations.

    Further for surface plasmons to exist you need excite the surface waves on the metals. What makes these phenomena interesting for optical applications is that in metals like silver and gold these are in the visible regime. I do not think that this is the case for the metals that are operating radio frequencies.
  6. Feb 8, 2012 #5


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    In the frequency range were antennas are used, the dielectric constant of the metal is of very large absolute value which means that the fields do not enter into the metal. What makes the plasmons interesting is that at the bulk plasmon frequency the dielectric constant vanishes and fields can enter the metal. If you now consider a tiny plasmonic waveguide, most of the field is inside the metal and not in the vacuum.
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