Polarisation is a phenomenon caused due to the wave nature of electromagnetic radiation. It is an important property of light that affects even those optical systems that do not specifically measure it. The polarisation of light affects the focus of laser beams, affects cut-off wavelengths of filters, and can be important to avoid unwanted back reflections. Read on to learn about polarisation and the two types of waves – Transverse and longitudinal.
Applications of polarisation
An example of polarisation in our everyday life is polaroid sunglasses. They minimise the glare caused by sunlight for drivers to see through windows and fishermen to see more clearly under the water surface. A few other applications of polarisation include:
- Three-dimensional movies that are produced and shown with the help of polarisation
- Seismology to study earthquakes
Longitudinal waves & transverse waves
Longitudinal waves are waves where the particles travel in the direction of motion of the waves. A sound wave is a classic example of a longitudinal wave. They cannot be polarised as they oscillate parallel to the direction of travel.
Transverse waves are waves where the particles oscillate perpendicular to the direction of the wave. These oscillations do not require a medium for propagation. An example of a transverse wave is the ripples on the water’s surface when you throw a rock. Light and all electromagnetic waves can be polarised.
Electromagnetic waves are transverse waves. Examples such as visible light and microwaves consist of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation. Light is called unpolarised if the direction of the electric field fluctuates randomly. Light sources such as sunlight, LED spotlights, and incandescent bulbs often emit unpolarised light. If the direction of the electric field of light is well defined, it is called polarised light. The most common source of polarised light is a laser.
The process of converting unpolarised light into polarised light is defined as polarisation. Waves can be polarised through a polariser or polarising filter.
Types of polarisation
- Linear polarisation: In linear polarisation, the electric field of light is confined to a single plane along the direction of propagation
- Circular polarisation: In circular polarisation, the electric field of light consists of two linear components that are perpendicular to each other, equal in amplitude, but has a phase difference of π/2. The propagation of the occurring electric field will be in a circular motion.
- Elliptical polarisation: In elliptical polarisation, the electric field of light follows an elliptical propagation. The amplitude and phase difference between to two linear components are not equal. This is the most general definition of polarised light, while circular and linear polarised light can be viewed as special cases of elliptically polarised light.
Polarisation is a fundamental property of electromagnetic waves that is related to many applications in our daily lives. If what you read above was interesting, you should enrol in a physics tuition class today! If your exams are approaching, our A level and O level physics tuition can clear all your doubts and help you do better.