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Second-order coherence – g2(t) of collision-broadened light and LEDs

  1. Jan 20, 2009 #1
    Hi. I have 2 questions about second-order coherence – g2(t):

    1) For collision-broadened light according to the literature g2(t)=1+|g1(t)|^2, where g1(t) is the 1st order coherence. Therefore for very low collision rate g1(t) =1 and thus g2(t)=2. However I would expect collision broadened light to reach a costant phase limit of CW for low collision rate and thus g2(t)=1. What did I miss here?

    2) In a light emitting diode – LED there should be many different scattering mechanisms for the radiating carriers and thus it should behave as a collision-broadened light g2(0)=2 with super-poissonian photon statistics. On the other hand the literature about LEDs talks about poissonian and even sub-poissonian photon statistics dependent only on the electron current and ignoring the scattering. Does anyone have a simple explanation of what should LED’s g2(t) look like and why?
  2. jcsd
  3. Jan 20, 2009 #2


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    Re: Second-order coherence – g2(t) of collision-broadened light and LEDs

    The above equation is an approximation for chaotic light, which is used to get g1 if g2 is known. It is not generally valid. If you go to the limit of low collision rates you also approach the monochromatic limit. In that case the light is not truly chaotic anymore and the above equation cannot be applied.

    Intensity correlation measurements are mostly measurements of noise. The properties of the emitted light from LEDs depend strongly on the kinds of noise present and how strong they are. There is not only noise due to scattering, but mostly due to the emission process itself and due to pump noise. If you have access to a good library, check the book "nonclassical light from semiconductor lasers and LEDs" by Kim, Somani and Yamamoto for a more detailed study.
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