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Questions about light

  1. Sep 10, 2008 #1
    If light passes through a fresnel lens and then through another lens focusing it a bit so it is not as concentrated (but still somewhat), and passes through a cold chamber, will the beam at the end still be hot, or will it be a bunch of low energy photons?
  2. jcsd
  3. Sep 10, 2008 #2


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    "Temperature" means nothing in empty space -- it's a number that describes the statistics of a bunch of particles considered together. If you pass the light through a "cold chamber," then you're passing the light through some kind of matter. That matter could do almost anything to it, and you haven't specified what kind of matter it is. Phosphors, for example, absorb high-energy photons and re-emit lower-energy photons.

    - Warren
  4. Sep 11, 2008 #3
    Carbon dioxide will be in the chamber. Is there a way to calculate the photons energy? Say the carbon dioxide is at -78º C. What other information do I need?
  5. Sep 18, 2008 #4
    I wouldn't expect the CO2 temperature to have any useful effect on the heat of the beam unless you're expecting the increased density at cold temperatures will scatter the light more. The energy present in a beam of light radiation is the amount of photons times the energy per photon, which is inversely proportional to wavelength. Energy of a photon is h*c/lambda

    I don't know what your application is, but you might look in to a "heat mirror". These will reflect the invisible infrared radiation that comes off of many light sources, and pass only the visible stuff.
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