A two-color femtosecond laser is transmitted in the air and a positive group velocity dispersion occurs. Negative group velocity dispersion is introduced when a-BBO crystal is added to the optical path. Can someone explain to me what is a positive group velocity dispersion and negative group velocity dispersion in simple sentences?
Hello Zhen,
the group velocity is the First derivative of the frequency w ( w= 2pi*f) to the wave vector k ( v = d w/ dk ). A positive group velocity means, that w increases with k, a negative means, that w decreases with k.
Y ours. R. Mitdank
The article given below may be helpful for understanding the negative group velocity dispersion .
https://arxiv.org/pdf/0807.4915
Hello, As Pr. Rüdiger Mitdank said, the group velocity is the First derivative of the frequency w ( w= 2pi*f) to the wave vector k ( v = d w/ dk ).
We deal hear with the dispersion of the group velocity which means its variation with k.
A positive group velocity dispersion means, that w increases with k, a negative means, that w decreases with k. This is the forward and direct explanation of negative/positive group velocity dispersion.
all the best
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