Slide 1
Polarization describes the electric field’s direction
Light is an electromagnetic wave. Polarization describes the behaviour of its electric-field direction as the wave travels.
More to Read
For a plane wave, the electric field oscillates perpendicular to the direction of travel. This transverse character allows orientations that ordinary longitudinal pressure waves in air do not share.
Slide 2
A linear filter selects one field component
A linear polarizer transmits an allowed electric-field component more readily than the perpendicular component. Rotating it changes which orientation passes.
More to Read
Unpolarized light contains rapidly varying field orientations. An ideal linear polarizer transmits half its average intensity, while real filters also absorb or reflect additional light depending on their construction.
Slide 3
Perpendicular filters can block the selected light
Two ideal linear polarizers with perpendicular transmission axes block the light passed by the first. Parallel axes allow that component through.
More to Read
At intermediate angles, transmitted intensity follows the square of the cosine of the angle for ideal polarizers. The first filter’s output, rather than the original unpolarized beam, is the input to this comparison.
Slide 4
Reflection makes some glare easier to filter
Reflection from a surface can polarize light. Polarizing sunglasses reduce some glare by rejecting a strongly represented orientation.
More to Read
The effect depends on incidence angle and surface properties. Reflections from water or roads are not all identically polarized, which is why rotating a filter changes some glare more than other parts of a scene.
Slide 5
Circular polarization lets the field direction rotate
Circular polarization has an electric-field direction that rotates as the wave progresses. Linear polarization is therefore only one possible state.
More to Read
Measuring polarization supplies information beyond brightness and colour. Instruments can use it to investigate scattering particles or material surfaces, because interactions can alter the incoming polarization in characteristic ways.