s- and p-polarizations 

These animations show the s (or 𝜎)- and p (or 𝜋)-polarizations relative to a surface. When the electric field (here, depicted in red) of an x-ray beam incident on a surface is (quasi-) perpendicular to the plane defined by the propagation direction and the surface normal, it is said to be 𝜎- or s-polarized (from the German for perpendicular, ‘senkrecht’). When the electric field lies in the plane, the radiation is 𝜋- or p-polarized (from the German for parallel, er, ‘parallel’). The matlab code lets the user choose between the two.