The vector of electric field in a linearly polarized electromagnetic wave (blue) oscillates only in one direction.  In circularly polarized wave the end of the vector of electric field  (red) moves in a spiral curve.

The light reflected from a specimen surface can change the state of polarization. This phenomenon underlies the principles of ellipsometry.

Microscopy with the use of the principles of ellipsometry. Sample and substrate reflect the light in different polarizations. Using polarizer we can visualize the sample and investigate its properties.

Malus' law. When a perfect polarizer is placed in a polarized beam of light, the intensity I of the light that passes through is given by equation I=I₀cos²θ, where θ is the angle between the light's initial polarization direction and the axis of the polarizer.