What is the polarization of light in physics? It is one of the most interesting and important phenomena in optics, which reveals the transverse nature of light.
Table of Contents
Introduction
Understanding the Wave Nature of Light and the Type of Motion.
Previously, interference and diffraction proved that light behaves like a wave. But these phenomena do not tell us the type of wave motion, such as;
- Longitudinal (like sound)
- Transverse (like waves on a string)
This is where polarization comes into play and gives us the answer:
The light wave is transverse in nature.
Understanding how light behaves is one of the key foundations of physical optics. This introductory topic breaks down the concept, types, and applications of polarization in a structured, easy-to-follow format.
What is Polarization of Light?
Polarization can be defined as:
“The process by which the electric and magnetic vibrations of light waves are restricted to a single plane of vibration”.
It is the property exhibited only by transverse waves, such as light waves. It does not occur for longitudinal waves such as sound waves.
Transverse Waves
Let us recall what a transverse wave is.
“A transverse wave is one where vibrations occur perpendicular to the direction of wave propagation”.
For instance, waves on a stretched string.
Vibrations in a Transverse Wave
These vibrations can occur in:
- A vertical plane
- A horizontal plane
- Any arbitrary plane
The transfer waves can be confined to a single plane, called the plane of polarization, and the wave is polarized.
Plane of Polarization
The plane of polarization is defined as the plane containing:
- The direction of vibration of the particles of the medium
- The direction of propagation
Polarization = Restricting Vibrations to a Single Plane
Only transverse waves (like light) can be polarized, not longitudinal waves (like sound).
Light as an Electromagnetic Wave
A light wave consists of:
- A varying electric field (E)
- A varying magnetic field (B)
Both fields oscillate perpendicular to each other and to the direction of propagation.
Unpolarized Light
Ordinary light sources emit vibrations in all possible planes, making the light unpolarized.
Examples
- Firelight
- Sunlight
- Candlelight
- Incandescent or fluorescent bulbs
Polarized Light
If the vibrations of the electric field are confined to one plane, the light becomes polarized.
Example
- Laser light
- LCDs
- Light passing through birefringent crystals
How Can Unpolarized Light Be Polarized?
An unpolarized light can be polarized by various means. The 3 most common methods include:
- Using a polarizing filter
- Using a polarizing beam splitter
- Using optical (birefringent) crystals
Polarizing Filter
A polarizing filter (often called a Polaroid sheet) is a material. It converts unpolarized light into polarized light by allowing vibrations to pass only in one direction and blocking all others.
How does it work?
When unpolarized light strikes a polarizer:
- Only the electric field (E) component parallel to the axis of the filter passes through
- All other components are blocked
The light emerging becomes linearly polarized.
Applications
- Polaroid sunglasses
- Camera filters
- LCD screens
Polarizing Beam Splitter
A polarizing beam splitter (PBS) is an optical device that separates unpolarized light into two polarized beams.
How does it work?
The PBS is designed in a manner that when an unpolarized light enters the beam splitter.
- When unpolarized light enters the PBS, the component with its electric field parallel to the plane of incidence is transmitted straight through; this is called p-polarization.
- The component with its electric field perpendicular to the plane of incidence is reflected at 90°; this is called s-polarization (senkrecht = perpendicular).
Applications
- Laser optics
- Optical communication
- Quantum optics experiments
- 3D cinema projection systems
Optical Crystals (Birefringent Crystals)
Certain crystals—such as calcite, quartz, mica, and tourmaline—are birefringent (double-refracting). They can produce polarized light by splitting unpolarized light into two rays polarized at right angles.
How does it work?
When unpolarized light enters a birefringent crystal, it splits into two separate beams:
Ordinary ray (O-Ray)
O-ray travels with a constant refractive index and obeys Snell’s law. It is polarized in one specific direction only.
Extraordinary ray (E-Ray)
Unlike O-ray, it travels with a direction-dependent refractive index. It also does not obey Snell’s law. E-ray is polarized in the perpendicular direction to the O-ray
Features of O–Ray and E–Ray
The two rays possess the following features:
- Travel at different speeds
- Follow different paths
- Polarized in mutually perpendicular planes
This process polarizes the light naturally.
Applications
- Optical mineralogy
- Polarization microscopy
- Nicol prism (made from calcite)
- Wave plates (quarter-wave, half-wave plates)
Quick Recall
| Method | How It Polarizes Light |
| Polarizing Filter | Blocks all directions of vibration except one → produces linearly polarized light. |
| Polarizing Beam Splitter | Splits unpolarized light into two beams: transmitted beam (vertically polarized) and reflected beam (horizontally polarized). |
| Optical Crystals (Birefringent Crystals) | Split unpolarized light into two beams polarized at right angles (ordinary ray and extraordinary ray). |
3 Types of Polarization
Mainly, there are three types of polarization in physical optics.
i. Linear Polarization
A linear polarization shows the following features:
- The simplest form of polarization
- The electric field vector oscillates in one plane only.
- It can be seen in light emerging from polarizing filters
Example
- Sunglasses that reduce glare
- Light passing through a Polaroid sheet
ii. Circular Polarization
In this type of polarization, the electric field rotates in a circle as the wave propagates.
There are two types of circular polarizations:
- Right-handed (clockwise rotation)
- Left-handed (counter-clockwise rotation)
Examples
- Light reflected from CDs and DVDs
- Used in 3D movie glasses
iii. Elliptical Polarization
It is a combination of linear and circular polarization where the electric field traces an ellipse.
Elliptical polarization occurs when:
- Electric field components differ in amplitude
- They differ in phase by an arbitrary angle
Example
- Light passing through a wave plate or stress plate
- Light scattered from certain materials (e.g., atmospheric particles)
- Circularly polarized light after passing through a retarder or compensator
Importance of Polarization
Polarization has widespread applications across science, technology, and industry.
Other Fields
Its applications go beyond this range and also include:
- Biology
- Chemistry
- Material science
- Communication systems
2 Major Applications of Polarization from Real Life
1. Sky Photography
A camera fitted with a polarizing filter can:
- Reduce glare and haze
- Block excessive bright white light
- Enhance the contrast of clouds and sky
- Improve overall photo quality
How does it work?
- Scattered sunlight in the atmosphere becomes partially polarized.
- The polarizer selectively blocks certain components, giving clearer and more vibrant photos.
2. Stress Analysis of Materials (Photoelasticity)
Polarized light helps engineers to:
- Determine stress distribution in materials
- Identify weak points prone to strain
- Study the optical properties of plastics, metals, and glass
How does it work?
- When stressed, materials change their optical behaviour, producing interference fringes.
- Analysing these patterns allows prediction of material performance under load.
Applications
- Engineering design
- Manufacturing
- Quality control
Conclusion
Polarization reveals the transverse nature of light. It opens the door to a vast range of applications, including photography, astronomy, medical imaging, material science, etc.
Understanding polarization not only deepens our knowledge of optics but also allows us to harness light in innovative and practical ways.
Frequently Asked Questions (FAQs)
What is the polarization of light in physics?
It is the phenomenon in which the vibrations of a transverse wave (such as light) are restricted to a single plane perpendicular to the direction of propagation.
Write the differences between polarized light and unpolarized light.
Unpolarized light has vibrations in many planes, while polarized light has vibrations in only one plane.
What is the unwanted light that interferes with vision termed as?
Unwanted light that interferes with vision is called glare or stray light. To reduce this glare, polarized sunglasses are used.
Why are Polaroid sunglasses better than ordinary sunglasses?
Polaroid sunglasses are better because:
- They reduce glare from horizontal surfaces (water, roads, snow).
- They block horizontally polarized light, which is the main contributor to glare.
- They improve visual comfort and contrast.
Ordinary sunglasses reduce intensity but do not selectively block glare.
Is light from the sky partially polarized? How is it so?
Yes, light from the sky is partially polarized.
Reason
Sunlight is scattered by air molecules (Rayleigh scattering). During scattering:
- The electric field components perpendicular to the scattering plane are stronger.
- Thus, the scattered light (sky light) becomes partially polarized, especially at 90° from the Sun.
Write down some applications of plane-polarized light.
The applications of plane polarized light include:
- Polarized sunglasses – reduce glare.
- Stress analysis in engineering – using a polariscope.
- Liquid crystal displays (LCDs).
- 3D movies – two polarized projections.
- Optical activity measurement – polarimetry (e.g., sugar concentration).
- Photography – polarizing filters enhance contrast.
How would the sky appear if there had been no atmosphere?
Without an atmosphere, there would be no scattering of sunlight, so:
- The sky would appear completely black, even during the daytime.
- The Sun would appear as a very bright disk against a black background.
Define the phenomenon of polarization of waves. How does polarization of electromagnetic waves occur? Also classify the polarization of waves.
Definition
It is the property of transverse waves in which the vibrations are confined to a single plane.
How EM waves become polarized
Electromagnetic waves consist of:
- Electric field (E)
- Magnetic field (B)
If the electric field oscillates in only one direction, the wave is plane-polarized. EM waves can be polarized by:
- selective absorption (Polaroids),
- reflection (Polarizing Beam Splitter)
- double refraction (Birefringent Crystals)
- scattering
Types of polarization
- Linear (plane) polarization
- Circular polarization
- Elliptical polarization
What is a Polaroid? Explain two main applications of polarization.
Polaroid is a polarizing material made of long-chain molecules aligned in one direction. It absorbs light vibrating parallel to the molecular direction and transmits light vibrating perpendicular to it. Thus, it produces polarized light.
Applications
- Sunglasses/filters – remove glare
- Polariscope – stress analysis
- LCD screens
- 3D movies
What is meant by optical activity? Discuss it.
Optical activity is the property of certain substances to rotate the polarizing plane of plane-polarized light passing through them.
Such substances are called optically active substances (e.g., sugar solution, quartz, turpentine).
Types of Optical Activity
There are two types:
- Dextrorotatory (D- or +) – rotate plane to the right.
- Laevorotatory (L- or −) – rotate plane to the left.
This phenomenon is used in:
- determining sugar concentration
- studying molecular structure
- chemical analysis