Polarisation of Light - SS2 Physics Lesson Note
Polarisation of light refers to the orientation of the electric field vector associated with light waves. When light waves undergo polarisation, the electric field vectors align in a particular direction.
Nature of Light:
Light is an electromagnetic wave that consists of oscillating electric and magnetic fields perpendicular to each other and to the direction of wave propagation. The behaviour of light can be described using both wave and particle (photon) models.
Transverse Nature of Light:
Light waves are transverse waves, meaning that the oscillations occur perpendicular to the direction of wave propagation. The electric field vector of light is responsible for many optical phenomena, including polarisation.
Polarisation States:
- Unpolarised Light: Ordinary light sources, such as the sun or a light bulb, emit unpolarised light. Unpolarised light consists of randomly oriented electric field vectors in all possible directions perpendicular to the direction of propagation.
- Polarised Light: When unpolarised light is passed through a polarising filter, it can be selectively polarised. Polarised light has electric field vectors aligned in a specific direction, resulting in a well-defined polarisation state.
Polarising Filters:
- Polarising filters are optical devices that can transmit light waves with specific polarisation orientations.
- A polarising filter consists of aligned molecules or microscopic openings that allow light waves with a particular polarisation direction to pass through while blocking or absorbing light waves with other polarisation orientations.
Types of Polarisation:
- Linear Polarisation: In linearly polarised light, the electric field vectors oscillate in a single plane perpendicular to the direction of wave propagation. This can be achieved by passing unpolarised light through a polarising filter.
- Circular Polarisation: Circularly polarised light has electric field vectors that rotate in a circular pattern as the wave propagates. This can be achieved by passing linearly polarised light through a quarter-wave plate or by using certain optical phenomena.
- Elliptical Polarisation: Elliptically polarised light has electric field vectors that trace out an elliptical path as the wave propagates. It is a combination of linear and circular polarisation.
Applications of Polarisation:
- Polarised sunglasses: Polarised sunglasses reduce glare by selectively blocking horizontally polarised light waves, improving visibility in bright conditions.
- Liquid crystal displays (LCDs): LCDs utilise the properties of polarisation to control the passage of light through liquid crystal materials, enabling the creation of images on screens.
- 3D glasses: Polarised 3D glasses use different polarisations to separate the left and right eye images, creating a three-dimensional perception.
- Communication technologies: Polarisation is utilised in various communication systems, such as satellite and wireless communications, to transmit and receive signals effectively.
Understanding polarisation is crucial in various fields of science and technology, including optics, telecommunications, and imaging. By manipulating the polarisation of light, researchers and engineers can develop innovative applications that rely on the selective control and detection of light waves with specific polarisation states.