Detecting visible light EM radiation with an antenna

  • Thread starter quitequick
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  • #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?
 

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  • #2
Drakkith
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Actually yes, but the antenna needs to be REALLY REALLY tiny.

http://en.wikipedia.org/wiki/Nantenna

The main problem is that the electric field oscillates so quickly that current electronics cannot operate fast enough to directly record the field.
 
  • #3
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Actually yes, but the antenna needs to be REALLY REALLY tiny.
By REALLY REALLY tiny, do you mean about the size of the photo receptors in our retina's?
 
  • #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.
 
  • #5
Drakkith
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By REALLY REALLY tiny, do you mean about the size of the photo receptors in our retina's?
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!".
 
  • #6
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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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