Refractive Index
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.. warning::
    This page is INCOMPLETE

The refractive index is a dimensionless number that gives an indication of how much light will bend in a medium.

While we typically deal with a real-valued refractive index, many materials have a complex refractive index which, where the real part is the standard refractive index, and the imaginary part is known as the optical extinction coefficient.  Vacuum will have a perfectly real refractive index of 1, while something like glass will have a very small extinction coefficient.  Metals have a very large extinction coefficient due to them being a conductor (and thus absorb incident electromagnetic waves extremely well as their free elections are free to oscillate with the incoming wave).
    

Snell's Law
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.. math::
    n_1 \sin{\theta_1} = n_2\sin{\theta_2}

where :math:`\theta_1` is the angle of incidence, and :math:`\theta_2` is the angle of refraction (both relative to the surface normal at the interface).