Optics- Polarisation Of Light - Electric Field & Intensity Of Light

Slide 1:

Optics- Polarisation of Light - Electric Field & Intensity of Light

Polarisation of light refers to the alignment of the oscillations of electric field vectors of light waves.
Light waves are transverse waves, which means the oscillations occur perpendicular to the direction of wave propagation.
Electric field vectors in unpolarised light oscillate in all possible planes perpendicular to the direction of propagation.
Polarisation can be achieved by passing light through certain materials, like polaroid filters.
The intensity of light is directly proportional to the square of the electric field amplitude.

Slide 2:

Polarisation by Reflection

When light waves strike a surface at a certain angle of incidence, they can become plane-polarised by reflection.
This angle is known as the Brewster’s angle.
Brewster’s angle is given by the equation: θ_B = arctan(n), where n is the refractive index of the medium.
At Brewster’s angle, the reflected light becomes completely polarised perpendicular to the plane of incidence.
This phenomenon is used in optical devices like polarising sunglasses.

Slide 3:

Polarisation by Double Refraction

Double refraction occurs when light passes through certain materials, like calcite crystals.
The incident light splits into two beams, known as ordinary and extraordinary rays.
The two rays have different refractive indices, and their vibrations occur in different planes.
The extraordinary ray is polarised perpendicular to the plane of incidence.
This property of double refraction is used in devices like polarising microscopes.

Slide 4:

Law of Malus

The intensity of polarised light transmitted through an ideal polariser is given by the law of Malus.
The law states that the intensity I of the transmitted light is directly proportional to the square of the amplitude E.
Mathematically, I = I_0 * cos^2(θ), where I_0 is the initial intensity of the light and θ is the angle between the polariser and the plane of polarisation.
The law of Malus holds true only for ideal polarisers.

Slide 5:

Optical Activity

Some substances have the ability to rotate the plane of polarisation of light passing through them.
This phenomenon is known as optical activity.
The angle of rotation depends on the thickness of the substance and the concentration of the solution.
Optical activity is observed in chiral molecules that do not possess a plane of symmetry.
It is commonly used in the analysis of sugar solutions.

Slide 6:

Polarisation of Electric Field

Electric field vectors in plane-polarised light oscillate in a single plane perpendicular to the direction of wave propagation.
The direction of the electric field is parallel to the direction of the plane of polarisation.
Different polarisation orientations can be achieved by rotating the polariser relative to the plane of polarisation.
The electric field amplitude remains constant, but the direction changes.
The intensity of polarised light is directly proportional to the square of the electric field amplitude.

Slide 7:

Polarisation of Light Waves

Light waves are transverse electromagnetic waves.
They consist of electric field vectors and magnetic field vectors oscillating perpendicular to each other and to the direction of wave propagation.
Polarisation refers specifically to the alignment of electric field vectors.
Polarisation can occur naturally, by reflection, or by passing light through polarising materials.
It has applications in various fields including optics, medicine, and communication.

Slide 8:

Natural and Artificial Polarisation

Natural polarisation occurs when light passes through certain natural substances with aligned molecules.
For example, sunlight scattered in the atmosphere becomes partially polarised due to scattering.
Artificial polarisation can be achieved by passing light through man-made polarisers like polaroid filters.
Polaroid filters consist of long-chain polymer molecules that preferentially absorb light polarised in specific directions.
They are commonly used in sunglasses, cameras, and LCD screens.

Slide 9:

Polarisation and Interference

Polarised light can undergo interference when two polarised beams overlap.
Interference occurs due to the superposition of the two waves.
The resultant intensity is dependent on the phase difference between the waves.
Constructive interference occurs when the phase difference is a multiple of 2π.
Destructive interference occurs when the phase difference is an odd multiple of π.

Slide 10:

Uses of Polarised Light

Polarised light has various applications in different fields.
In microscopy, polarised light can reveal the internal structure of transparent objects.
In photography, polarising filters are used to reduce glare from reflective surfaces.
Polarised sunglasses help reduce glare and improve visibility by selectively blocking horizontally polarised light.
LCD screens work on the principle of polarisation to control the passage of light.
Polarisation also plays a crucial role in 3D movie technology.

Slide 11:

Polarising Filters

Polarising filters are optical devices that selectively transmit light waves with a specific polarisation orientation.
They consist of a material that absorbs or reflects light polarised in certain directions.
By rotating the filter, we can control the transmitted polarisation direction.
Examples of polarising filters include polaroid sheets, polarising sunglasses, and wave plates.
They are widely used in photography, optics, and other applications requiring control over light polarisation.

Slide 12:

Malus’ Law Equation

Malus’ law describes the relationship between the intensity of polarised light transmitted through a polariser and the angle between the polariser and the plane of polarisation.
The equation for Malus’ law is given by:
- I = I₀ * cos²(θ)
  - I is the transmitted intensity
  - I₀ is the initial intensity
  - θ is the angle between the polariser and the plane of polarisation.
This equation helps us understand how the transmission of polarised light varies with the angle of the polariser.

Slide 13:

Polarisation by Refraction

When light undergoes refraction at an interface, the refracted ray can become partially polarised.
This polarisation arises due to a preferential alignment of the electric field vectors.
The amount of polarisation depends on the angle of incidence and the refractive indices of the media involved.
Brewster’s law gives the condition for maximum polarisation by refraction:
- tan(θᵦ) = n₂/n₁,
  - θᵦ is the Brewster’s angle
  - n₁ and n₂ are the refractive indices of the two media.

Slide 14:

Polarisation by Scattering

When light interacts with small particles or surfaces, it undergoes scattering.
Scattered light can become partially or fully polarised, depending on the scattering angle and the size of the particles.
Rayleigh scattering is a type of scattering that occurs when the size of the scattering particles is much smaller than the wavelength of light.
Scattered light from Rayleigh scattering is partially polarised, with the electric field vibrations perpendicular to the plane of incidence.

Slide 15:

Polarisation by Absorption

Some materials selectively absorb light waves with specific polarisation orientations.
This absorption leads to the polarisation of transmitted light.
Examples of materials that exhibit polarisation by absorption include iodine-stained polyvinyl alcohol films and dichroic crystals.
The absorbed light has its electric field component aligned with the absorbing molecules, resulting in polarisation.

Slide 16:

Polarisation and Optical Instruments

Polarisation plays a crucial role in various optical instruments.
Polarising microscopes use polarised light to examine birefringent materials and observe their optical properties.
Analyzers and polarizers are used in spectroscopy to control the polarisation of light for accurate measurements.
Polarimetry devices utilize polarisation to analyze molecular structures and determine their concentrations in solutions.
Optical devices, such as wave plates and retarders, manipulate polarisation for specific applications, such as controlling light phase shifts.

Slide 17:

Polarisation in 3D Glasses

3D glasses employ polarisation to create the illusion of depth perception in movies or video games.
The glasses consist of different polarising filters for each eye.
The movie or game is projected using two images, each polarised with a different orientation.
The glasses ensure that the left eye sees only the left image, and the right eye sees only the right image.
This separation results in a stereoscopic effect, enhancing the perception of three-dimensional objects.

Slide 18:

Analyzing Light with Polarised Filters

Polarised filters are widely used to analyze and manipulate light in scientific research and practical applications.
By using successive polarisers with specific orientations, we can analyze the polarisation state of incoming light.
When two polarisers are crossed (perpendicular to each other), no light passes through if the incident light is completely polarised.
By inserting additional polarisers at different angles, we can determine the polarisation orientation and intensity of the incident light.

Slide 19:

Circular and Elliptical Polarisation

Circular and elliptical polarisation occur when the electric field vectors of a light wave rotate as the wave propagates.
Circular polarisation refers to the case where the magnitude of the electric field vector remains constant, but its direction rotates.
Elliptical polarisation occurs when the magnitude and direction of the electric field vectors change as the wave propagates.
Circular and elliptical polarisation are produced by superposing two perpendicular waves with amplitudes that differ in phase and magnitude.

Slide 20:

Applications of Circular Polarisation

Circular polarisation finds applications in various fields:
- 3D movie projection: Circular polarisation is used to separate left-eye and right-eye views for 3D movies.
- Optical communication: It minimizes interference and signal degradation caused by reflections or misalignment.
- Medical imaging: Circular polarisation can enhance the contrast and detail of tissues in certain imaging techniques.
- Astronomy: Circular polarisation is used to study the properties of celestial objects such as pulsars and active galactic nuclei.
- Material analysis: Circular polarisation is employed in spectroscopic techniques to investigate molecular structures.

Slide 21:

Polarised Light and Reflection

When polarised light is incident on a reflecting surface, the reflected light becomes partially polarised.
The angle between the plane of polarisation of the incident light and the plane of incidence determines the degree of polarisation of the reflected light.
When the two planes are perpendicular to each other, the reflected light is completely polarised.
The reflected light is partially polarised when the two planes make an angle other than 90 degrees.
The degree of polarisation can be determined using the Law of Malus.

Slide 22:

Polarisation by Scattering

Scattering of light is the process by which a small fraction of incident light is redirected in different directions due to interaction with small particles or irregularities in the medium.
When unpolarised light scatters, it becomes partially polarised.
Rayleigh scattering, which occurs when the size of the scatterers is much smaller than the wavelength of light, leads to polarisation of the scattered light.
The degree of polarisation in Rayleigh scattering depends on the angle of scattering and the wavelength of light.

Slide 23:

Polarised Light and Optical Instruments

Polarised light is extensively used in optical instruments such as polarising microscopes, spectroscopes, and ellipsometers.
Polarising microscopes use polarised light to observe the optical properties of materials, particularly birefringent crystals.
Spectroscopes utilize polarisation to control and analyze the light passing through different substances for accurate measurements.
Ellipsometers measure the polarization state of light reflected or transmitted through a sample to determine its optical properties.
These instruments are invaluable in scientific research, material analysis, and various industries.

Slide 24:

Polarisation Filters in Medicine

Polarisation filters find applications in the medical field for diagnosing certain conditions.
Polarised light can help detect skin disorders like melasma by analyzing changes in skin pigmentation and blood flow.
Polarised light is also used in ophthalmology to diagnose eye abnormalities, such as corneal disorders and cataracts.
Polarisation imaging techniques aid in the early detection of cancerous tissues and improve surgical precision in tumor removal.
The use of polarised light in medicine continues to evolve, offering valuable insights into physiological processes.

Slide 25:

Optical Rotatory Power

Optical rotatory power refers to the ability of certain substances to rotate the plane of polarisation of incident light.
This rotation occurs due to the interaction between light and chiral molecules in the substance.
The amount of rotation depends on the concentration of the substance, the length of the path traveled by light, and the wavelength of light.
Optical rotatory power is measured using a polarimeter and is expressed in terms of the specific rotation or angle of rotation per unit length.

Slide 26:

Polarisation and Communication

Polarised light plays a crucial role in optical communication systems.
Fiber optic cables use polarisation to transmit information encoded in light signals.
By modulating the polarisation of light, data can be encoded and transmitted through the optical fiber.
Polarisation-maintaining fibers ensure that the polarisation state of the transmitted light remains stable and aligned.
The use of polarised light in communication systems allows for high-speed data transmission with minimal interference.

Slide 27:

Stress Analysis with Polarisation

Polarisation techniques are employed in stress analysis to determine stress distribution in materials.
When a transparent or semi-transparent material is subjected to stress, the refractive index changes.
By polarising light and passing it through the stressed material, stress-induced birefringence can be observed.
Analysis of the resultant patterns can provide insights into stress concentration, fracture mechanics, and material behavior under loading.
Polarisation-based stress analysis techniques are widely used in mechanical engineering and material science.

Slide 28:

Polarisation and 3D Photography

Polarisation is used in 3D photography to capture stereo images.
Two images of the same scene are captured, each with a different polarisation orientation.
These images are then viewed using corresponding polarised glasses, which deliver the separate images to each eye.
The brain combines the two images, creating a perception of depth and three-dimensionality.
Polarisation-based 3D photography provides a realistic and immersive viewing experience.

Slide 29:

Liquid Crystal Displays (LCDs)

Liquid crystal displays (LCDs) utilize polarisers and liquid crystals to create images and videos.
An LCD screen consists of a backlight, polariser filters, liquid crystal layer, and another set of polarisers.
The liquid crystals align according to the applied electric field, determining the polarisation of light passing through.
By manipulating the alignment of liquid crystals, individual pixels can control the amount of light transmitted, forming images.
Polarisation control in LCDs allows for high-resolution and energy-efficient displays used in televisions, smartphones, and computer screens.

Slide 30:

Summary

Polarisation of light refers to the alignment of electric field vectors in light waves.
Polarised light can be achieved through reflection, absorption, scattering, and double refraction.
The degree of polarisation is determined by the angle of incidence, the properties of the material, and the wavelength of light.
Polarised light finds diverse applications in optics, medicine, communication, materials analysis, and imaging technologies.
It is used in optical instruments, 3D technology, stress analysis, optical communication, and various medical diagnostics.
Polarisation techniques enhance our understanding of light and enable numerous practical applications.