Polarizer

When the two polarization states are relative to the direction of a surface (usually found with Fresnel reflection), they are usually termed s and p. This distinction between Cartesian and s–p polarization can be negligible in many cases, but it becomes significant for achieving high contrast and with wide angular spreads of the incident light.

Its current H-sheet form is made from polyvinyl alcohol (PVA) plastic with an iodine doping.

The durability and practicality of Polaroid makes it the most common type of polarizer in use, for example for sunglasses, photographic filters, and liquid crystal displays.

A modern type of absorptive polarizer is made of elongated silver nano-particles embedded in thin (≤0.5 mm) glass plates.

[5] Such glass polarizers perform best for long-wavelength infrared light, and are widely used in fiber-optic communication.

A simple linear polarizer can be made by tilting a stack of glass plates at Brewster's angle to the beam.

[6] Adding more plates and reducing the angle allows a better compromise between transmission and polarization to be achieved.

In these crystals, a beam of unpolarized light incident on their surface is split by refraction into two rays.

A Nicol prism was an early type of birefringent polarizer, that consists of a crystal of calcite which has been split and rejoined with Canada balsam.

At the internal interface, an unpolarized beam splits into two linearly polarized rays which leave the prism at a divergence angle of 15°–45°.

Thin-film linear polarizers (also known as TFPN) are glass substrates on which a special optical coating is applied.

Either Brewster's angle reflections or interference effects in the film cause them to act as beam-splitting polarizers.

Since the electrons are free to move in this direction, the polarizer behaves in a similar manner to the surface of a metal when reflecting light, and the wave is reflected backwards along the incident beam (minus a small amount of energy lost to Joule heating of the wire).

Overall, this causes the transmitted wave to be linearly polarized with an electric field completely perpendicular to the wires.

Therefore, it is relatively easy to construct wire-grid polarizers for microwaves, far-infrared, and mid-infrared radiation.

In addition, advanced lithographic techniques can also build very tight pitch metallic grids (typ.

Since the degree of polarization depends little on wavelength and angle of incidence, they are used for broad-band applications such as projection.

A beam of unpolarized light can be thought of as containing a uniform mixture of linear polarizations at all possible angles.

If the two axes are orthogonal, the polarizers are crossed and in theory no light is transmitted, though again practically speaking no polarizer is perfect and the transmission is not exactly zero (for example, crossed Polaroid sheets appear slightly blue in colour because their extinction ratio is better in the red).

They are used as polarizing filters in photography to reduce oblique reflections from non-metallic surfaces, and are the lenses of the 3D glasses worn for viewing some stereoscopic movies (notably, the RealD 3D variety), where the polarization of light is used to differentiate which image should be seen by the left and right eye.

The transmission axis of the linear polarizer needs to be half way (45°) between the fast and slow axes of the quarter-wave plate.

In the arrangement above, the transmission axis of the linear polarizer is at a positive 45° angle relative to the right horizontal and is represented with an orange line.

In the illustration toward the right is the electric field of the linearly polarized light just before it enters the quarter-wave plate.

Directly below it, for comparison purposes, is the linearly polarized light that entered the quarter-wave plate.

Similarly this light is considered counter-clockwise circularly polarized because if a stationary observer faces against the direction of travel, the person will observe its electric field rotate in the counter-clockwise direction as the wave passes a given point in space.

In trying to appreciate how the quarter-wave plate transforms the linearly polarized light, it is important to realize that the two components discussed are not entities in and of themselves but are merely mental constructs one uses to help appreciate what is happening.

First, given the dual usefulness of this image, begin by imagining the circularly polarized light displayed at the top as still leaving the quarter-wave plate and traveling toward the left.

This brings the two components back into their initial phase relationship, reestablishing the selected circular polarization.

However, cameras with through-the-lens metering (TTL) and autofocusing systems – that is, all modern SLR and DSLR – rely on optical elements that pass linearly polarized light.

If light entering the camera is already linearly polarized, it can upset the exposure or autofocus systems.

A polarizing filter cuts down the reflections (top) and makes it possible to see a photographer through the glass at roughly Brewster's angle although reflections off the back window of the car are not cut because they are less-strongly polarized, according to the Fresnel equations .
A stack of plates at Brewster's angle to a beam reflects off a fraction of the s -polarized light at each surface, leaving a p -polarized beam. Full polarization at Brewster's angle requires many more plates than shown. The arrows indicate the direction of the electrical field, not the magnetic field, which is perpendicular to the electric field.
A wire-grid polarizer converts an unpolarized beam into one with a single linear polarization . Coloured arrows depict the electric field vector. The diagonally polarized waves also contribute to the transmitted polarization. Their vertical components are transmitted (shown), while the horizontal components are absorbed and reflected (not shown).
A Nicol prism
A Wollaston prism
Malus' Law where θ 1 − θ 0 = θ i
Malus' Law demonstration. No light can pass through a pair of crossed polarizing filters, but when a third filter is inserted between them with its axis not parallel to either one, some light can pass.
Image is well described in article
Circular polarizer creating left-handed circularly polarized light. It is considered left-handed as viewed from the receiver and right-handed as viewed from the source. [ 11 ]
Three vertical sin waves
Linearly polarized light , represented using components, entering a quarter-wave plate . The blue and green curves are projections of the red line on the vertical and horizontal planes respectively.
The top image is left-handed/counter-clockwise circularly polarized, as viewed from the receiver. [ 11 ] The bottom image is that of linearly polarized light . The blue and green curves are projections of the red lines on the vertical and horizontal planes respectively.
Animation of left-handed/counter-clockwise circularly polarized light (left-handed as viewed from the receiver [ 11 ] )
Circular polarizer passing left-handed, counter-clockwise circularly polarized light (left-handed as viewed from the receiver) [ 11 ]
Left-handed/counter-clockwise circularly polarized light displayed above linearly polarized light . [ 11 ] The blue and green curves are projections of the helix on the vertical and horizontal planes respectively.
Homogeneous circular polarizer passing left-handed, counter-clockwise circularly polarized light (left-handed as viewed from the receiver) [ 11 ]