How to define the plane of incidence for normal incidence

[fannyfanfanz]

How to define the plane of incidence for normal incidence of a plane polarized wave?
Is the reflection coefficient defined by ordinary, extraordinary, or the combination of both waves?

Thanks for the help!

 

[UltrafastPED]

The usual method is to define one line with the wave vector (normal to the plane wave), which is then fixed by a point of incidence at the material surface. The vector normal to the surface at that point gives you a second vector ... these then define the plane of incidence. The k-vector for the reflected wave will be in this plane.

If the wave vector is normal to the surface there is no unique plane of incidence.