Why self focusing at high densities?

[Kidphysics]

I understand it has something to do with the index of refraction being directly related to the intensity of radiation, but on a more fundamental level, why?

 

[Vanadium 50]

What are you talking about?

 

[Kidphysics]

http://en.wikipedia.org/wiki/Self-focusing I thought it would be known I guess instead of densities I meant high intensity self focusing.

 

[0xDEADBEEF]

The index of refraction depends on the square root of the dielectric constant, which describes how a material polarizes when there are electric fields present. Polarization is an effect where electrons and nuclei are pulled apart. If the intensity of the electric field becomes very high there are non-linear effects and often once the electrons are pulled far from the nuclei they can be moved more easily leading to a higher dielectric constant and thus a larger index of refraction.

 

[Kidphysics]

Thank you very much for the reply. I should have been more clear from the start. Your last sentence really helped me out and makes sense. My only remaining question is exactly how and why does the index of refraction depend on the square root of the dielectric constant..