Polarisation Of Light

Polarisation is changing unpolarized light (in which particles vibrate in various planes) into polarised light(light waves that vibrate in a single plane). Plane polarised light is made up of waves with the same direction of vibration for all of them.

Light is the interaction of electric and magnetic fields travelling through space. A light wave’s electric and magnetic vibrations occur perpendicularly to each other. The electric field moves in one direction and magnetic in another, though always perpendicularly. So, we have one plane occupied by an electric field, the magnetic field perpendicular to it, and the direction of travel which is perpendicular to both. These electric and magnetic vibrations can occur in numerous planes.

What are the types of Polarisation?

There are three types of polarisation based on transverse and longitudinal wave motion:

Linear Polarisation – Linear polarisation or plane polarisation of electromagnetic radiation is a confinement of the electric field vector to a given plane along the direction of propagation.

Elliptical Polarisation – It is a type of polarisation in which, at every point, the electromagnetic field has a constant magnitude. Still, its direction rotates with a constant value in a plane perpendicular to the direction of the wave. A circularly polarised wave can rotate in two ways, either the electric field vector rotates according to the direction of propagation in a right-hand direction or the direction of propagation in a left-hand sense. The phenomenon of polarisation rises as a result of the fact that light acts as a 2 Dimensional transverse wave.

Circular Polarisation – The electric field of light has two linear components that are perpendicular to each other and have identical amplitudes, but the phase difference is π ⁄ 2. The electric field that occurs will propagate in a circular motion.

Methods for Polarisation

Light can be polarised in a few different ways :

By using Polaroids :

We can observe a plane of vibration parallel to the plane in the diagram below. There is also a vibration plane that is perpendicular to the plane. The first picture is not polarised. The second picture is polarised, meaning it is perpendicular or parallel to the first. So let’s start with polaroids to understand polarisation.

Polaroids are polarising materials made up of molecules oriented in a specific direction. A pass axis exists on every Polaroid. Only the pass axis will enable light to flow through. Both the horizontal and vertical pass axes can exist on a polaroid. These determine the way light passes through it. When the light that is not polarised travels through a polaroid, it becomes polarised.

Polarisation by Scattering

When light strikes a molecule or an atom, the light energy is absorbed and re-emitted in multiple directions. Polarisation causes this scattering. Furthermore, the emitted light travels in many directions.
When unpolarised light is incident on a particle, we obtain dispersed light. As a result, when unpolarised light travels through a molecule, the light is polarised in the direction perpendicular to the incident ray. As a result, light polarisation occurs in this direction.
Furthermore, dispersed light has complete polarisation, but light travelling through molecules has partial polarisation.

Polarisation by Reflection and Refraction

The incident ray reflected ray, and refracted ray may all be seen in the diagram below. Unpolarised light is visible on the incident beam. The unpolarized light is depicted in the diagram above. The dot denotes perpendicular directions, whereas the lines denote parallel directions.

Most of the reflected ray’s light is polarised parallel to the plane, with only a few exceptions. In contrast, most of the light in a refracted beam is unpolarized, with one or two polarised components. As a result, we can see that the reflected and refracted rays are both partly polarised.

Application of Polarisation

Some of the major applications of polarisation are :

• In anti-glare sunglasses.
• Polaroid filters are used for stress analysis tests on transparent plastics.
• Differentiation between transverse and longitudinal waves is done via polarisation.
• In the entertainment industry, to telecast or to show a 3D film, the phenomenon of polarisation of light is used.
• To cut the refractions, fishermen, skiers, motorists,and sportsmen need special sunglasses. In the production of these special sunglasses polarisation of light is used.
• Many photographers use polarizers to capture the perfect scene.
• Polarisation microscopes are used in geological studies to identify minerals.
• In infrared spectroscopy.
• To check the chirality of organic compounds.
• To study the physics of the early universe, the effect of polarisation is used.
• To know the source of radiation and scattering.
• To characterise the stress-strain distribution in the prototypes, polarisation is used.
• To identify thermally tempered lenses.
• In ophthalmic instruments, to eliminate strong reflection from a patient’s cornea, the phenomenon polarisation of light is used.
• As light passes through the atmosphere polarisation of light is observed
• The scattered light is known to give rise to various colours in the sky.

FAQs on Polarisation of Light