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Archived Intensity of coherent/incoherent light

  1. Mar 11, 2014 #1
    Here's a question I'm working on. I've managed everything uptil the first bolded part, then I get stuck there. I have no idea how to estimate the relative intensities of coherent and incoherent light. I've had a look at tonnes of formulas for the intensity of light but can't find one which would work here. Any help?

    And for the second part I've made bold, is the answer to that question: photon energies and coherence of the emitted light do not change?

    Question: In a 3-level laser device two different energies of light are emitted. Coherent light is observed with a wavelength of 2700nm and incoherent light with a wavelength of 694nm. Use the above information to sketch the energy levels of the 3-level laser system. Label the energies (in eV) of each of the excited levels relative to the ground state. You may assume that the lowest energy level is the ground state of the atom.

    If an optical flash is used as the mechanism to excite the three level laser system what wavelength of light should be used?

    Estimate the relative intensity of the coherent and incoherent light produced by the laser.

    Consider a situation in which the photon density of the lasing cavity is very significantly reduced, for example by reducing the reflectivity of the surfaces of the lasing cavity. How would you expect the photon energies and coherence of the emitted light to change?
  2. jcsd
  3. Feb 6, 2016 #2


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    The photon energies don't change, but spontaneous emission in the lower transition can become relevant.

    I guess the 694 nm are from the pumping process, so they go from the highest to the intermediate state, while 2700 nm corresponds to the difference between intermediate and lowest state. This also means up to one emitted pumping-related photon per laser photon.
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