Velocity of light in water cloud

[woody726]

If laser energy travels through a non-homogeneous cloud, does the velocity changes with the cloud density as well or only due to the different than air index of refraction?

 

[HallsofIvy]

At what "level" do you want this considered? That is, if you are thinking about the cloud as a single object the light is going through, then the density is included in the index of refraction. If you are considering each drop of water separately, the speed through each drop depends only on the index of refraction, but then the overall speed depends upon how many drops the light goes through- i.e,. the density.