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Anomalous Dispersion?

  1. Jun 14, 2007 #1
    Anomalous Dispersion???

    All I know about anomalous dispersion is that it has a negative second order propagation vector.
    That would mean the refractive index is negative...how???

    How do you also "achieve" or get "into" the anomalous dispersion regime?
     
  2. jcsd
  3. Jun 14, 2007 #2

    Meir Achuz

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    The group velocity of a wave is given by
    [tex]v_g=\frac{c}{n}\left(1+\frac{\lambda}{n}\frac{dn}{d\lambda}\right)[/tex].
    This means when [tex]dn/d\lambda[/tex] is positive, the group velocity could be greater than c. The refractive spectrum would also be reversed. For these reasons, [tex]dn/d\lambda>0[/tex] is called "anomalous dispersion".
    n is still usually postive, but the lambda derivative is positive.
    Anomalous dispersion usually occurs near a resonant frequency of the material, where n varies rapidly with wavelength. Because of this rapid variation, [tex]v_g[/tex] does not represent the propagation velocity of a pulse, so that relativity is not violated.
     
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