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Optical Noise Photons

  1. Nov 25, 2014 #1
    I need this information for a simulation I am working on that involves optical photon detectors.

    Specifically, I need a rough figure for how many photons a photon detector would register per second if I were to place it in ambient light from the sun.

    I realize that this number depends on the bandwidth of the detector and its quantum efficiency at different wavelengths, but lets assume I have tight bandwidth in the green part of the spectrum (say less than 100nm) with a very sharp roll off.

    Would the detector saturate? Or is the amount of ambient photons low enough to register a good number?

    I'm thinking I may be able to calculate a rough number based on how much radiation the sun shines on the earth over the bandwidth I need. I probably will try this later, but I figured I would ask to get a number I can compare with.
     
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  3. Nov 25, 2014 #2

    Andy Resnick

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  4. Nov 25, 2014 #3

    Drakkith

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    What exactly is "ambient" light from the Sun?
     
  5. Nov 26, 2014 #4

    Thank you for your reply. These links will definitely be useful when I do a theoretical analysis.

    What I was hoping for is an experimenter that has access to photon counter that can tell me what it registers when it is out in normal lighting conditions outside. Does the detector saturate?



    Light from the sun on Earth. As in, bring the detector outside.


    Sorry if this is kind of a weird question, I just need a general figure of how many "noise photons per second" I should expect from outdoor lighting conditions, say on a sunny day.
     
  6. Nov 27, 2014 #5

    Drakkith

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    Okay, but there's a big, big difference between having the detector in direct sunlight or having it under a shady overhang. Both are outside, but direct sunlight will probably saturate your sensor in less than a second depending on what kind of sensor you have.
     
  7. Nov 27, 2014 #6

    e.bar.goum

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    Call me an experimentalist, but why not just measure it?
     
  8. Nov 27, 2014 #7

    Drakkith

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    Hush! Experimentalists aren't allowed to speak! Now back to the closet with you!
     
  9. Nov 27, 2014 #8

    Danger

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    Not to mention what's going on in the atmosphere. Green is the most effective "carrier" colour under water, but less so in air. So, even just in that tiny regard, cloud cover and humidity would affect how much green gets to your detector.
     
  10. Nov 27, 2014 #9
    PVlighthouse's spectrum library has a calculator for finding the photon flux for a given wavelength range. From that it's simple to find the number of photons.
     
  11. Nov 27, 2014 #10

    Danger

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    Bookmarked. Thanks for that.
     
  12. Nov 28, 2014 #11

    Andy Resnick

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    No sane owner of a photon counter is going to take it outside and use it during the day.
     
  13. Dec 2, 2014 #12
    Thank you!! This is what I need!!

    Haha. Well at the moment, I do not have access to any equipment.

    Thanks for all the replies!
     
  14. Dec 3, 2014 #13
    Look up insolation. You should be able to find average solar power near where you live. You can assume that the spectrum is fairly close to a black body during mid-day. (If you need more than a rough estimate, you'll have to factor in scattering effects on the spectrum, but then you'd be better off just measuring the thing.) From the insolation and the spectrum, you can calculate the photon flux. Of course, you need to adjust based on the angle of your detector to the sun (simply cos(theta)).
    Integrate the photon flux * the quantum efficiency of your detector to get the counts/second. Good CCDs have quantum efficiencies > 80%. Compare that count to the well depth of your detector or your ADC max counts.
     
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