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Light - stopped or trapped inside a crystal?

  1. Jul 25, 2013 #1
    Light -- stopped or trapped inside a crystal?

    In the below experiment:


    Opaque crystal of yttrium silicate doped with praseodymium

    1. Is light stopped or trapped (i.e. internally reflecting, bouncing off the "walls")?

    2. Will quantum coherence be preserved as long as the photon stays inside the crystal?

    3. Is light "slowed" in water because of absorption and re-emittance of the photon?
    Last edited: Jul 25, 2013
  2. jcsd
  3. Jul 25, 2013 #2
  4. Jul 25, 2013 #3


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  5. Oct 3, 2013 #4
    I'm bumping this thread in hopes that somebody has an answer regarding this experiment. Thanks!
  6. Oct 3, 2013 #5
    San K,
    Read the Wikipedia article on Electromagnetically induced transparency. You will see that the answer to your question 1 is no. The answer to question 2 is yes. As far as question three goes; when light passes from a medium of lower refractive index to a medium of higher refractive index, the group velocity slows down. This is a completely different optical process from EIT.
  7. Oct 4, 2013 #6
    With regards to your specific question f.wright above me answered it correctly, but I can still expand on these results a bit.

    Slowed and stopped light of pulses happens when the dispersion profile contains very steep slopes, as the group velocity of a pulse inside a medium depends on the derivative of the group refractive index with respect to frequency. In addition, one can see that while the pulse is being slowed down by this effect, an increasing part of its energy is actually stored in the material. A kind of pseudoparticle is formed, called a polariton, which is a coupled system of a photon and a material excitation. Stopped light is a special case when all of the energy has been converted into the material. Hope that makes things a bit more clear.
  8. Oct 4, 2013 #7
    Thanks Zargon, f.wright and coktail.

    Good introduction to the term "polariton"
  9. Oct 5, 2013 #8
    can the converted energy be held (in the material) for upto to, say, an hour and then later re-converted back as a photon? .....that emits out of the material
    Last edited: Oct 5, 2013
  10. Oct 7, 2013 #9
    Yes, in principle it can, it depends on the coherence time of the material. In the quoted paper, the hyperfine levels of Praseodymium is used, which have a max of about 1 minute, which they reach. But there are other rare-earth elements which can be used as well, for example Europium where the theoretical coherence time is several days.
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