Polarisation

Polarisation Of Light

Polarisation is defined in physics as a phenomenon induced by electromagnetic radiation’s wave nature and is characterised as a phenomenon caused by electromagnetic radiation’s wave nature. Another word for this phenomenon is the polarisation effect. In the case of sunlight, which is an electromagnetic wave, the path from the Sun to the Earth is facilitated by a vacuum. When an electric field interacts with a magnetic field, electromagnetic waves are generated, so they are called electromagnetic waves. This part will introduce you to transverse and longitudinal waves, which will be discussed further in this text. Additionally, polarisation and plane polarised light will be covered, which will be helpful in the future.

Light is produced when electric and magnetic forces interact in space. A light wave’s electric and magnetic vibrations are antithetical. The direction of electrical fields is always perpendicular to that of magnetic fields. An electric field perpendicular to a magnetic field perpendicular to both planes results. Field vibrations occur in multiple planes

Polarisation occurs when unpolarised light is converted to polarised light. Electric and magnetic fields vibrate in all directions simultaneously in unpolarised light but not in polarised light.

Different Types of Polarisation

Polarisation can be divided into three types based on transverse wave motion.

• Linear Polarisation

Linear polarisation of electromagnetic radiation, or plane polarisation, refers to a restriction of the electric field vector or magnetic field vector along the propagation path. Augustin-Jean Fresnel created the term linear polarisation (French: polarisation rectiligne) in 1822. 

The electric and magnetic fields oscillate in a linearly polarised light wave in perpendicular directions. Electric field vibrations are regarded to be in the polarisation direction. Polarisation can occur in any direction perpendicular to the wave’s axis. The polarisation is not rationally different when it is rotated by 180 degrees.

• The elliptical polarisation

As the name suggests, this type of polarisation is where the electric field vector defines an ellipse in the direction of propagation in any fixed plane. An elliptically polarised wave can be split into two linearly polarised perpendicular waves. For elliptical polarisation the electric field of the light consists of two linear components that are perpendicular to each other, they have a phase difference not equal to π/2. Elliptically polarised waves reveal chirality because the electric field can spin clockwise or anti-clockwise while propagating.

• Circular Polarisation

In this case, electromagnetic polarisation has a constant amplitude, but its direction rotates with a constant value in a plane perpendicular to the wave’s trajectory. The electric field vector of a circularly polarised wave can either rotate in a right-hand direction or a left-hand direction, depending on the propagation direction. Because light acts as a two-dimensional transverse wave, polarisation occurs.  For circular polarisation the electric field of the light consists of two linear components of same amplitude that are perpendicular to each other and have a phase difference of π/2.

The techniques for polarisation

There are various methods to achieve Polarisation of light, but these four are the most popular.

• polarisation by scattering
• polarisation by reflection
• polarisation by refraction
• polarisation by transmission

1. Polarisation 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 polarisation, and they cause glare by transmitting partially polarised light.

2. Polarisation by reflection

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

3. Polarisation 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 polarisation within the refracted beam. Refraction by polarisation is a phenomenon most frequently observed in perpendicular planes.

4. Polarisation by transmission 

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

Specifications & Applications of Polarisation

Some examples of polarisation applications include the following.

• Chemists who study organic molecules and establish their chirality are said to be practising chiral chemistry, a field of chemistry that uses polarised methods to accomplish this task.
• We can distinguish between longitudinal and transverse waves thanks to polarisation information.
• Stress analysis with Polaroid filters is a common practice in the plastics industry.
• Three-dimensional films are created and displayed with the help of polarisation.
• A glare-reducing technology, polarisation is used in sunglasses to reduce glare and reflection.
• The study of earthquakes is carried out using this method in seismology.
• It is possible to improve the resolution of infrared spectroscopy data by employing polarisation.

Key points

• Polarisation refers to wave oscillations having a distinct direction concerning the wave’s propagation direction. Electromagnetic waves (EM waves) are transverse waves that can be polarised. Polarisation is defined as the direction parallel to the EM wave’s electric field.
• Unpolarised light comprises a large number of rays with random polarisation directions. Light can be polarised by passing through a polarising filter or another polarising substance. 
• Reflection can also cause Polarisation. Scattering can also create polarisation. Numerous optically active compounds exist that rotate the polarisation direction of light travelling through them.

Conclusion

Light polarisation plays an important role in many optical applications. When it comes to optical design, the wavelength and intensity of light are typically given more consideration than their polarisation. Although optical systems that do not explicitly measure polarisation are affected by it, polarisation is a crucial feature of light.

With regards to laser beam focus and filter wavelength cut-off, the polarisation of light may have a significant impact. If you want to do stress analysis in glass or plastic and analyse medicinal ingredients, you’ll need a microscope. LCD panels, 3D movies, and glare-reducing sunglasses all benefit from the ability to absorb multiple polarizations of light.