Optical Radiation

  1. Assume you have a sinusoidal 500THz function generator and assume you have a compatible antenna. If you feed the signal to your antenna, is optical phenomena observable ?
    Last edited: Jul 19, 2012
  2. jcsd
  3. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    In this experiment a generator capable of emitting electromagnetic radiation at 500THz would be a laser: probalby either a gas or solid-state laser. Without calculation we can say that since 474 THz is the optical frequency of a helium-neon laser, then the 500Thz would appear to the human eye red.
  4. No that's not why I meant.

    Time-varying electric currents flowing through a conductor radiates electromagnetic fields at the same frequency. If a 500THz function generator (electrical signal output) is fed to a conductor at appropriate size, can human eye observe the emission ?
  5. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    y33t, sorry, I jumped to some conclusion. This is from Wikipedia:

    "Terahertz radiation is a region of the spectrum between far infrared and microwaves. Until recently, the range was rarely studied and few sources existed for microwave energy at the high end of the band (sub-millimeter waves or so-called terahertz waves), but applications such as imaging and communications are now appearing. Scientists are also looking to apply terahertz technology in the armed forces, where high-frequency waves might be directed at enemy troops to incapacitate their electronic equipment. [15]

    [15] The interaction between high-intensity, ultra-short laser pulses and plasmas leads to the emission of coherent, short-pulse radiation at terahertz frequencies. A device is developed that can use the short-pulse radiation at terahertz frequencies to deactivate any electronic systems many miles away and create a virtual shield for any advancing army, navy or air force.
  6. You are not event close to what I am talking about... (:
  7. russ_watters

    Staff: Mentor

    What is an appropriate size...?
  8. Drakkith

    Staff: Mentor

    I would think so. But such a setup is not possible with current technology. The frequency is much too high.
  9. Appropriate size that will fit (in length) to the high frequency signal, let's say around 500nm.
    Last edited: Jul 29, 2012
  10. That's correct today technology is not capable of generating this scale of frequencies.

    What would be the interpretation from wave-particle duality approach in this phenomena ? Will there be photons ?
  11. Drakkith

    Staff: Mentor

    What? Why wouldn't there be? There are always photons if an EM wave is generated.
  12. Then please enlighten me ; assume there is a 500nm antenna and our imaginary 500THz signal is fed to this antenna. How exactly will the antenna look like ? Will it glow ? Glow from the core of the antenna or from the surface ? Assuming an omni-directional antenna ; will it glow homogeneously through the antenna length ?
  13. mfb

    Staff: Mentor

    You cannot observe details of a ~500nm-antenna with visible light of 500nm wavelength, at least not without fancy metamaterials which would probably change the way the antenna emits light in a significant way.
    You will see a spot of light, even with the best microscopes.
  14. The CCD can easily detect the output of the antenna. Surely this depends on the amplitude of the signal fed to antenna.
  15. There must be some sort of limit based on the mean time between collisions of electrons in a conducting wire. I don't see how you could make electrons oscillate with such speed if they don't have time to actually interact with one another?

    Solid state physics is definitely my weak point but I'm struggling to come up with a fundamental reason why this shouldn't be possible.
  16. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    Y33t, sevgili dostum,

    I’m not sure this will enlighten you. I am slightly confused by your questions. You have proposed the application of a 500Terahertz (THz) signal to an antenna of 500 nanometer (nm) in length.

    When I calculate the wavelength of 500 THz EM radiation signal I get about 600 nm. This is called submillimeter radiation (in astronomy) and is not visible to the human eye.

    Furthermore, when I calculate the frequency of EM radiation of 500 nm I get about 600 THz. This is what’s known as “blue-green visible light”.

    I am sure you have already seen seven different types of Terahertz radiation generators at: http://en.wikipedia.org/wiki/Terahertz_radiation
    None of these THz generators produce radiation that is visible.

    I may be totally wrong with my above calculations because I am not schooled in quantum optics. Will you please try to help me understand your experiment?
  17. mfb

    Staff: Mentor

    Bobbywhy: 600µm is sub-millimeter, and 1000 times longer than 600nm. 600nm is similar to 500nm, just a different color (the visible range is roughly 400-800nm).
    THz generators generate ~1THz, not 500.
  18. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    mfb, thank you for the clarifying explanations.
  19. 500THz correspnds to visible orange light in air. The antenna should be 600 nm. No idea if it would work. Guess you would need a bunch of them to see them. No idea about the electons in the wire. Maybe not using metal conductors would be the answer. I wonder how such a nano antenna could be made.
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