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## Main Question or Discussion Point

Hey ppl,

I have a question for you.

For the case of light propagation in the air the the group-velocity dispersion parameter D is infinity because the derivative of the group velocity should be a zero (group velocity is constant ; w=ck and Vgroup=dw/dk). Who can explain me this? dispersion parameter is infinity meaning that the pulse will spread very fast. I never thought about that question but maybe I'm wrong. Plz clarify me that point.

formula for D parameter you can find here:

http://en.wikipedia.org/wiki/Dispersion_(optics)

I have a question for you.

For the case of light propagation in the air the the group-velocity dispersion parameter D is infinity because the derivative of the group velocity should be a zero (group velocity is constant ; w=ck and Vgroup=dw/dk). Who can explain me this? dispersion parameter is infinity meaning that the pulse will spread very fast. I never thought about that question but maybe I'm wrong. Plz clarify me that point.

formula for D parameter you can find here:

http://en.wikipedia.org/wiki/Dispersion_(optics)