The standard optics definition for P & S polarizations is shown in the diagram below.

Note: For some reason, companies that make ruled, surface relief, and reflection gratings define P & S polarizations as just the opposite of this.  The standard optics definition is:

	Es = When the electric field vector is perpendicular to the plane of incidence, the light is said to be S-Polarized (TE).
	Ep = When the electric field vector is parallel to the plane of incidence, the light is said to be P-Polarized (TM).