Polarization

Introduction

Many optical applications require an understanding and manipulation of polarization. It is not uncommon for optical designers to overlook the polarization of light when designing lenses and optical components. Even optical systems without explicit measurement of it are affected by the phenomenon of polarization. A light’s polarization influences its focus, its cutoff wavelength and may even affect unwanted back reflections. These methods are used, for instance, in handling stress in glass or plastic, in analyzing pharmaceutical ingredients, and in biological microscopy. Likewise, materials can absorb different polarizations of light to varying degrees, an important property of LCD screens, 3D movies, and glare-reducing sunglasses. The polarized filters have their utility in the plastic industry.

In physics, the phenomenon of Polarization occurs due to electromagnetic radiation’s wave nature.Sunlight is an example of electromagnetic waves since sunlight travels through the vacuum to reach the Earth. Due to the presence of interacting electric fields and magnetic fields they are called electromagnetic waves. 

An oscillation’s geometrical orientation is written as its polarization; a property applied to transverse waves. A transverse wave oscillates in a perpendicular direction to its motion. Vibrations traveling along a taut string, such as those found in musical instruments such as a guitar string, are polarized transverse waves. If the string is plucked vertically or horizontally or at an angle perpendicular to the string, the vibrations will be in a vertical or horizontal direction. Waves that propagate longitudinally, such as sound waves in a gas or liquid, are polarized since the particles in the oscillation are transported along the propagation direction. Electromagnetic waves, such as radio waves and light waves, gravitational waves, and transverse sound waves (shear waves) are examples of transverse waves with polarization.

Transverse waves

‘Transverse waves are waves, i.e., particle motion within the wave is parallel to the wave’s motion direction. For example, when you throw a stone, ripples are created in the water. 

When particles of the medium move longitudinally, they are said to be longitudinal waves.

Electromagnetism and electric fields interact to create light. Light waves vibrate perpendicularly, both electrically and magnetically. While magnetic and electric fields always move perpendicularly, the electric field always moves in one direction. The electric field occupies one plane and is perpendicular to the magnetic field, as is the direction of travel. Both magnetic and electric vibrations may occur in multiple directions. There are several possible planes of vibration in unpolarized light. Sunlight, lamps, and tube lights emit unpolarised light. 

Polarized waves are another type of wave. In polarized waves, the vibration occurs in one plane only. All waves in plane-polarized light are symmetrical in their vibration direction.  

Types of Polarization of Light

The polarization of light is classified into three types according to its transverse and longitudinal wave movement.

• • Linear polarization
  • Circular polarization

• Elliptical polarization

1.   Linear Polarization 

Light waves which are linearly polarized vibrate in a linear direction perpendicular to the wave axis, while magnetic fields vibrate perpendicular to both the advancement axis and the direction of the electronic field. Polarization indicates the direction of electric field vibration. Other directions perpendicular to the wave axis can also result in polarization. It is not rationally different to rotate the polarization by 180°.

2.   Circular Polarization

An electromagnetic field rotates in a plane parallel to the wave’s direction so that, at every point, its magnitude is constant, but its direction rotates constantly. The electric field vector of a circularly polarized wave can rotate either left-handedly or right-handedly, depending on the direction of propagation. A characteristic of light is that it acts as a transverse wave in two dimensions, hence the phenomenon of polarization.

3. Elliptical Polarization 

In this type of polarization, the tip of the vector describing the electric field traverses a fixed plane and is normal to the direction of propagation. Rectangular waves can be elliptical polarized bifurcated into two linearly polarized waves with their polarization planes perpendicular to each other. Elliptically polarized waves exhibit chirality because the electric field can rotate clockwise or counter-clockwise during propagation.

Circular polarization is a special case of elliptical polarization, just as a linear polarization is a special case of elliptical polarization.

Methods of Polarization of Light

Polarization of light can be achieved through various methods, but these four are the most popular.

• Polarization by Scattering
• Polarization by Reflection
• Polarization by Refraction
• Polarization by Transmission

1. Polarization by Scattering 

The electromagnetic waves produced by the movement of light through a medium are caused by the vibration of the medium’s atoms (also dust present in the medium). The light is scattered as a result of these waves radiating outward. Light waves are absorbed and re-emitted throughout the entire process. The scattered light is also called partial polarization. They cause glare by transmitting partially polarized light.

2. Polarization by Reflection 

In the case of unpolarized light falling at a particular angle on a nonmetallic surface, the surface reflects the polarized light. To regulate the magnitude of polarization, angles of incidence and non-metallic surfaces play an important role in this process.

3. Polarization by Refraction 

The refraction of light is the act of changing the direction and speed of a light wave as it travels from one medium to another. In doing so, there is polarization within the refracted beam. Refraction by polarization is a phenomenon most frequently observed in perpendicular planes.

4. Polarization by Transmission 

A filter material with a special chemical composition is used in this method. The filters are called Polaroids. Polaroids block electromagnetic waves on one of their two axes. In a single plane, these polaroid filters let the light that is unpolarized transmit half of its vibrations. Polarized light has half the intensity.

Polarization Applications

Polarization can be applied in the following ways:

• Polarized sunglasses reduce glare
• To perform stress analysis tests in the plastic industry, Polaroid filters are used
• Polarization is used to create and show three-dimensional movies
• Transverse and longitudinal waves can be distinguished by polarization
• Polarization is utilized in infrared spectroscopy
• Seismologists use it to study earthquakes
• Chemists use polarization techniques to determine the chirality of organic compounds 

Conclusion

It is both natural and artificial sources of light that produce light. The phenomenon of light is definitely one of the waves. Objects are affected by the waves. Waves can interfere and diffract. In order to reach us, the light waves must travel through the vacuum, where they are converted into electromagnetic waves by Earth’s magnetic field. They are transverse waves. There are reflections, refractions, interferences, diffractions, double refractions, and polarization. Light waves travel in all directions, both in electric and magnetic fields. It is known as the Polarization of light when the vectors move within a single plane. According to the direction of propagation, these beams are filtered with special materials.