 Vertical polarization

Vertical polarization is linear polarization of an electromagnetic wave whose electric field oscillates along a chosen vertical direction transverse to propagation. The reference direction is part of the specification; for a horizontal free-space beam it is often set by gravity or an instrument axis.

A rotatable polarizer and photodetector test this direction: an ideal analyzer aligned vertically transmits the beam, while a horizontal analyzer extinguishes it. The labels vertical and horizontal describe a basis, not intrinsic properties independent of geometry. For a beam propagating vertically, another transverse reference must be specified.