Paper Example on Types of Polarizers

Introduction

A polarizer or in other words polarisers is a device used in converting mixed-polarization or unpolarized beams of electromagnetic waves for example light into a beam that is in the state of a single polarization either circular, linear or elliptic. Polarizers applications include some optical instruments and techniques as well as polarizing filters which can be located in applications like LCD (Liquid Crystal Display) technology, photography and polarizing sunglasses (Azo Optics, 2007). Apart from light for example microwaves, radio waves and X-rays, polarizers can also be made for other electromagnetic types of waves. The most common classification of polarizers includes circular polarizers and linear polarizers. Reflected lights can be controlled off a subject by polarizers from a particular angle averting unwanted light from getting into the lens and therefore impacting in images with color saturation and high contrast levels (Canon, 2018).

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Types of Polarizers

As mentioned above, polarizers are commonly classified into two types:

• Linear polarizers
• Circular polarizers

Linear Polarizers

It can be further divided into two categories: absorptive and beam-splitting polarizers (Azo Optics, 2007). In absorptive polarizers, the states of the unwanted polarization are soaked up (absorbed)by the device while on the other hand, in beam splitting polarizers, the unpolarized or mixed beam is split into two beams with the states of opposite polarization. Polarizers that maintain and manage similar polarization axes with an angle of incidence variation over time are usually referred as cartesian polarizers because the vectors of the polarization can be defined based on cartesian coordinates (such as vertical vs. horizontal) that have an independent polarizer-oriented surface. Based on Fresnel reflection that will be explained at-length below, two states of polarization that are respective to surface direction are known as s and p. Despite of the negligibility of the s-p polarization and cartesian distinction, its essentiality comes in when achieving incident light of wide angular spread and high contrast.

Absorptive Polarizer - Polarization by Absorption

Various crystalline materials soak up more light compared to another in one incident plane; thus, in those materials, the light progressing is more polarized throughout the process. This absorption anisotropy is called dichroism. Some dichroic elements are naturally occurring and also commercial polaroid materials that polarize through selective absorption. Dichroic materials are crystalline materials with distinct absorption abilities for incident perpendicular planes for light. A commonly known natural dichroic material is the mineral tourmaline. The crystal of a tourmaline comprises of a unique axis (optic) that offers strong absorption when any electric vector field is perpendicularly incident to the axis. Polaroid also, on the other hand, can be defined as a strong dichroic material thus effective and efficient polarizer. There is no light transmission if the ideal polarizer's transmission axes are perpendicular. Other angles light transmissions are under Law of Malus. Law of Malus states that the polarized beam plane light intensity varies after it passes via a rotatable polarizer as the square of the cosine angle at which the rotating polarizer from the position is giving maximum intensity (Hyper Physics, n.d.).

Polaroid material is the most used and well-known dichroic material that absorbs light selectively from one plane, usually transmitting light via polaroid sheet less than 1% though, in a perpendicular plane, the transmitted light can be more than 80%. To most, Polaroid is termed as polaroid H-sheet that is iodine (impregnated polyvinyl alcohol) sheet. Polyvinyl alcohol sheet in one direction is heated and stretched while softening which as a result align the molecules of the long polymeric in the stretch direction. The iodine atoms chain themselves when immersed in iodine to the aligned chains and provide electrons that are not perpendicular to the iodine atoms but can easily move along the aligned chains. The iodine electron in action in the aligned chain's impact to dissipative effects that facilitates strong absorption in electric- light waves fields that is parallel to these aligned chains. The perpendicular direction to the chains of polyvinyl alcohol can be referred to as pass direction given the iodine electrons with no free motion in the chains cannot absorb energy.

The Polaroid cost-effectiveness, practicality, and durability are what makes it well known as the commonly used type of polarizer for example for photographic filers, sunglasses, and liquid crystal displays. In sunglasses, the polaroid material used uses either selective absorption or dichroism to attain polarization as illustrated in the figure below. The modern absorptive polarizer contains silver Nano-particles which are elongated and embedded in 0.5 mm thin glass plates. These modern polarizers types are more durable compared to the plastic polaroid film and also can absorb more light thus its polarization attainment is as much higher- 100,000: 1 and its correct light absorption of as low as 1.5%. This modern absorptive polarizer is mostly used in optical fiber communications and perform better for infrared light of short wavelength.

Beam-Splitting Polarizers

Beamsplitters, as mentioned above, splits the incident beam light into two different beams at a designated proportion and vice versa (combining two distinct beams to a single beam). Most common classification of beam splitters is in accordance to their construction: plate and cube beam splitters as shown in the figure below (Edmund Optics, 2019). For a polarizing beamsplitter which is ideal, it should be polarized wholly with orthogonal polarizations though to most only one of the two split beam lights are polarized fully while the other one comprises polarization mixture states. Different from polarization by absorption, polarization by beam splitting does not require light absorption and dissipation of the rejected polarization state energy thus beamsplitters polarizers can be used effectively and suitable with laser light due to high beams intensity. Also, it can be used in a situation where the components of the two polarization are to be used simultaneously or is to be analyzed. A beamsplitter is an essential part of interferometers. It can be further discussed under the following properties: Fresnel reflection, birefringent crystal properties such as calcite and quartz, thin film and WGP (Wire- Grid Polarizers).

Circular Polarizers

Also termed as circular polarizing filters. It can be utilized in the creation of light that is circularly polarized or pass counter-clockwise and clockwise and selectively absorb light which is circularly polarized. The light of a circular polarizer comprises of two different perpendicular planes that are of electromagnetic waves with 900 phase difference and equal amplitude. The light is either defined as right-circularly or left- circularly polarized light depending on the source view angle on the rotation of the electric vector that is either counterclockwise or clockwise respectively. A complete revolution of the electric field vector can be defined as one wavelength of light towards you (Hyper Physics, n.d.). Circularly polarized light can also be as a result of linearly polarized light passage via a quarter-wave plate at a 45o angle to the plate optic axis. A circular polarizer is used in photography as polarizing filters to cut down non-metallic surfaces' oblique reflections, and also, they are the 3D glasses lenses worn during stereoscopic movies viewing especially the variety of RealD 3D where light polarization is utilized in image differentiation- which image to be seen by right and left eye.

Applications of Polarization

One of the main applications of polarization knowledge is a polarizing filter in photography. Photography applied first the concept of linear polarizing filters and still can be implemented on non-reflex and older SLRs (Single- Lens reflex cameras). Nowadays, cameras with autofocusing and TTL (through-the-lens metering) systems- modern DSLR and SLR, depends significantly on optical components that allow linearly polarized light to pass through. In case the entering light to the camera is polarized linearly already, there may be exposure upset or autofocus systems. A circular polarizing filter, on the other hand, stops light that is linearly polarized thus can be applied in removing reflections or darkening skies; however, the passed circularly polarized light does not damage TTL systems (Ang, 2008).

Conclusion

In conclusion, the above research paper describes in-depth the concept behind polarizers- its definition, various polarizers types that is circular and linear polarizers, its multiple applications mainly in photography and the application of Law of Malus. Generally, plane wave light in space is defined as linearly polarized light while when the light consists of two plane waves with a different phase of 90o and equal amplitude, then the light is referred as a circular polarizer. However, if the two different plane waves differ in related amplitude phase by 90o or 90o then is known as an elliptic polarizer.

References

Ang, T. (2008). Fundamentals of Modern Photography. Octopus Publishing Group Limited. P168. ISBN 978-1-84533-2310.

Azo Optics. (2007). Polarizer- Basic Definition and Types of Polarizers. Retrieved from; https://www.azooptics.com/Article.aspx?ArticleID=49

Canon. (2018). The Application of Polarizers. Retrieved from; https://www.canon.com.hk/en/club/article/itemDetail.do?itemId=10297&page=1

Edmund Optics. (2019). What are Beamsplitters? Retrieved from; https://www.edmundoptics.com/resources/application-notes/optics/what-are-beamsplitters/

Hyper Physics. (n.d.). Classification of Polarization. Retrieved from; http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polclas.html

Hyper Physics. (n.d.). Polarization Absorption. Retrieved from; http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polabs.html