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Detecting visible light EM radiation with an antenna

  1. Jan 21, 2013 #1
    If visible light is part of the EM spectrum just like radio waves, is it possible to construct a radio like antenna (metal pronged structure) to detect them?
  2. jcsd
  3. Jan 21, 2013 #2


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    Actually yes, but the antenna needs to be REALLY REALLY tiny.


    The main problem is that the electric field oscillates so quickly that current electronics cannot operate fast enough to directly record the field.
  4. Jan 21, 2013 #3
    By REALLY REALLY tiny, do you mean about the size of the photo receptors in our retina's?
  5. Jan 21, 2013 #4


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    About the size of the wavelength, some hundred nanometers (about 0.0000005 meters)
    Our photo receptors are not classical antennas, and their active molecules are even smaller than the wavelength.
  6. Jan 21, 2013 #5


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    From the wiki article I linked:

    The wavelengths in the solar spectrum range from approximately 0.3-2.0 μm.[3] Thus, in order for a rectifying antenna to be an efficient electromagnetic collector in the solar spectrum, it needs to be on the order of hundreds of nm in size.

    I don't know how large the molecules in our eyes are that actually detect the light, so I can't give you a comparison. The cells themselves are much larger than the wavelength, but only the molecule size matters I believe. Still, they aren't even antennas. They just absorb EM energy and change shape without determining any details about the light other than "Hey, I got a photon!".
  7. Jan 21, 2013 #6
    That's right... see here

    Ultimately, the absorption of a photon causes a bent molecule to straighten out. If this happens enough times within a short period and a very localized region (spatial/temporal summation), the net activity is enough to depolarize a membrane to originate a neural signal.
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