Optics- Polarisation Of Light - Unpolarised Light-Passing Through A Polariser

Optics- Polarisation of Light - Unpolarised Light-Passing through a Polariser

Light emitted from most sources such as the Sun, light bulbs, and lasers is unpolarised.
Unpolarised light consists of electromagnetic waves vibrating in all possible directions perpendicular to the direction of propagation.
When unpolarised light passes through a polariser, it becomes polarised.
A polariser is a material that allows light with vibrations in only one direction to pass through it.
The intensity of the transmitted polarised light is reduced by a factor of $\frac{1}{2}$ when compared to the incident unpolarised light.

Optics- Polarisation of Light - Unpolarised Light-Passing through a Polariser (Contd.)

The transmitted light is said to be linearly polarised as its electric field vectors oscillate in a single plane.
The orientation of the polariser determines the final polarisation direction of the transmitted light.
The intensity of the polarised light transmitted through a polariser depends on the angle between the plane of polarisation of the incident light and the orientation of the polariser.
When the plane of polarisation of the incident light is perpendicular to the polariser, no light is transmitted.

Optics- Polarisation of Light - Unpolarised Light-Passing through a Polariser (Contd.)

The intensity of the transmitted light is given by Malus’ law:
- $I = I_0 \cos^2(\theta)$
- where $I$ is the transmitted intensity, $I_0$ is the incident intensity, and $\theta$ is the angle between the plane of polarisation of the incident light and the orientation of the polariser.
The transmitted intensity reaches a maximum when the plane of polarisation of the incident light is aligned with the polariser (i.e., when $\theta = 0$).
The transmitted intensity is zero when the plane of polarisation of the incident light is perpendicular to the polariser (i.e., when $\theta = 90°$ or $\theta = \pi/2$ rad).

Optics- Polarisation of Light - Unpolarised Light-Passing through a Polariser (Contd.)

The transmitted light may also undergo a change in color when polarised.
Certain polarisers can filter out specific colours of light, causing the transmitted light to have a different colour from the incident light.
Polarised sunglasses make use of this property to reduce glare and improve visibility.
The sunglasses have a filter that selectively transmits only horizontally polarised light, blocking vertically polarised light.
This helps in reducing the glare caused by horizontal reflections of sunlight.

Optics- Polarisation of Light - Unpolarised Light-Passing through a Polariser (Contd.)

Polarised light is widely used in various scientific applications and technologies.
Some common applications of polarised light include:
- Analyzing the composition and structure of various materials.
- Reducing glare in photography and cinematography.
- Communication systems using polarisation-based modulation techniques.
- Optical sensors and devices utilizing the unique properties of polarised light.
- Studying the behavior of light in liquid crystals, which are crucial for display technologies like LCD.

Optics- Polarisation of Light - Unpolarised Light-Passing through a Polariser (Contd.)

Polarisation of light is a fundamental concept in physics and plays a crucial role in understanding various optical phenomena.
It provides insights into the behavior of light waves as they interact with different materials and objects.
Understanding polarisation is essential for advanced topics in optics, such as interference, diffraction, and polarization filters.
The study of polarised light is not only limited to physics but also finds applications in engineering, telecommunications, and other related fields.
As we progress further in this course, we will explore more fascinating aspects of optics and the intriguing properties of light.

Unpolarised Light and Polarisation:

Light emitted from most sources is unpolarised.
Unpolarised light consists of electromagnetic waves vibrating in all possible directions perpendicular to the direction of propagation.
Polarisation refers to the process of restricting the vibrations of light to occur in a single plane.
A polariser is a material that can achieve this polarisation process.

Polarisers:

A polariser is a material with aligned molecules that can absorb or transmit light waves based on their orientation.
The most commonly used polariser is a polarising filter made from a special type of polymer with aligned microcrystals.
The alignment of these microcrystals allows only light waves with a specific polarisation direction to pass through.
The orientation of the polariser determines the final polarisation direction of the transmitted light.

Malus’ Law:

Malus’ Law describes the relationship between the incident intensity of unpolarised light and the intensity of the polarised light transmitted through a polariser.
It is given by the equation: $I = I_0 \cos^2(\theta)$, where I is the transmitted intensity, I₀ is the incident intensity, and θ is the angle between the plane of polarisation of the incident light and the orientation of the polariser.

Maximum Transmitted Intensity:

The transmitted intensity reaches its maximum when the plane of polarisation of the incident light is aligned with the polariser (θ = 0).
In this case, the transmitted intensity is equal to the incident intensity (I = I₀).

Minimum Transmitted Intensity:

The transmitted intensity is zero when the plane of polarisation of the incident light is perpendicular to the polariser (θ = 90° or θ = π/2 rad).
In this case, no light is transmitted through the polariser.

Intermediate Angles:

For intermediate angles between 0 and 90 degrees, the transmitted intensity is always less than the incident intensity.
The intensity decreases as the angle between the plane of polarisation and the polariser’s orientation increases.

Selective Transmission and Polarised Sunglasses:

Certain polarisers can selectively transmit specific colours of light, filtering out others.
Polarised sunglasses make use of this property to reduce glare caused by reflections of light.
The sunglasses have a polarising filter that selectively transmits horizontally polarised light, reducing horizontally polarised glare.

Applications in Material Analysis:

Polarisation of light is crucial in analyzing the composition and structure of various materials.
By studying polarised light interactions with materials, scientists can gain insights into their molecular arrangement and optical properties.
This helps in fields like chemistry, materials science, and semiconductor research.

Applications in Photography and Cinematography:

Polarised light is used in photography and cinematography to reduce glare and unwanted reflections.
By using polarising filters on cameras, photographers can selectively block polarised light reflecting off surfaces like water or glass, enhancing the overall image quality.

Applications in Communication Systems:

Polarisation-based modulation techniques are used in communication systems to transmit and receive information.
The polarisation states of light waves can be modulated to represent digital data, enabling efficient data transmission in optical fiber networks. ``

Applications in Optical Sensors and Devices:

Polarised light is utilized in various optical sensors and devices.
Optical sensors designed to detect specific molecular interactions or changes in materials often use polarised light to enhance sensitivity and accuracy.
Polarisation-based devices, such as polarisation filters, are used to control the intensity and direction of light in optical systems.

Applications in Liquid Crystal Displays (LCD):

Liquid crystal displays (LCD) are widely used in electronic devices like televisions, smartphones, and computer monitors.
LCDs make use of the unique properties of polarised light and liquid crystals.
The liquid crystals align themselves in response to an electric field, and polarisers control the orientation of polarised light, determining which pixels are illuminated and creating the displayed image.

Polarisation and Interference:

Polarisation plays a crucial role in understanding interference phenomena.
When polarised light passes through certain materials, it is split into two perpendicular polarisation components.
These components can interfere with each other, leading to constructive or destructive interference, producing distinct interference patterns.

Polarisation and Diffraction:

Diffraction is the bending, spreading, and interference of light waves as they pass through an aperture or around an obstacle.
Polarised light can undergo diffraction, producing polarisation-dependent diffraction patterns.
The polarisation state of the diffracted light can be analysed to determine the properties of the diffracting object.

Polarimetry:

Polarimetry is the measurement of the polarisation state of light.
It is used in various scientific and industrial applications to study the optical properties of materials, identify contaminants, measure molecular orientation, and more.
Polarimetry is based on the analysis of how the transmitted or reflected light interacts with polarisers and other optical components.

Optical Isolators and Circulators:

Optical isolators and circulators are devices that allow light to flow in one direction while preventing or redirecting light in the opposite direction.
These devices, commonly used in fiber optics and telecommunications, leverage the specific properties of polarised light to achieve their functionality.

Optical Retarders and Wave Plates:

Optical retarders, also known as wave plates or phase plates, are used to control the phase difference between two orthogonal polarisation states of light.
They can shift the phase of one polarisation component relative to the other, leading to changes in the overall polarisation state of transmitted light.
Wave plates find applications in optics, lasers, microscopy, and other areas.

Polarisation in Nature:

Polarisation of light is not limited to artificial sources and applications; it can also be observed in nature.
Reflection, scattering, and transmission of light through natural materials, such as water, ice, or biological tissues, can result in polarised light.
Understanding polarisation in natural systems helps scientists study and interpret various natural phenomena.

Future Developments and Research in Polarised Light:

Research in the field of polarised light is continuously advancing, leading to new discoveries, technologies, and applications.
Ongoing studies focus on developing more efficient polarisation-based devices, improving polarisation imaging techniques, and exploring the potential of polarised light in quantum information processing.
Polarised light continues to be an active area of research and innovation in the field of optics.

Summary and Review:

In this lecture, we explored the concept of unpolarised light passing through a polariser and becoming polarised.
We learned about Malus’ Law that relates the incident and transmitted intensities of polarised light.
We discussed various applications of polarised light, including material analysis, photography, communication systems, and liquid crystal displays.
Lastly, we touched upon the role of polarisation in interference, diffraction, and polarimetry, as well as its significance in natural phenomena and ongoing research.
Make sure to review the key concepts and examples covered in this lecture to solidify your understanding of polarised light. ``