27.8 Polarization
3 min read•june 18, 2024
Electromagnetic waves have a hidden property called . It's all about how the electric field wiggles as the wave moves. Understanding this helps us see why sunglasses work and how LCD screens light up.
We can make and use light in cool ways. Filters can create it, reflections can produce it, and even the sky scatters it. This knowledge lets us build better sunglasses, sharper displays, and tools to measure stress in materials.
Polarization of Electromagnetic Waves
Polarization of electromagnetic waves
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- describes the orientation of the electric field vector in an electromagnetic wave
- In a polarized wave, the electric field oscillates in a specific direction perpendicular to the wave propagation direction
- The magnetic field is always perpendicular to both the electric field and the wave propagation direction
- Types of polarization include linear, circular, and elliptical
- occurs when the electric field oscillates in a single plane (vertical or horizontal)
- involves the electric field vector rotating in a circular motion, either right-handed (clockwise) or left-handed (counterclockwise)
- occurs when the electric field vector traces an elliptical path
- light consists of waves with random polarization directions (sunlight, incandescent bulbs)
- Polarization is a property of , which include electromagnetic waves across the
Methods of producing polarized light
- selectively transmit light with a specific polarization
- absorb one polarization component while transmitting the other (Polaroid filters made of polyvinyl alcohol with embedded iodine crystals)
- split light into two orthogonally polarized components (calcite crystals, Nicol prisms)
- Reflection can produce polarized light when light reflects off a surface at
- Brewster's angle is given by , where and are the refractive indices of the two media (air and water)
- Scattering by small particles () can partially polarize light
- Blue sky light is partially polarized due to scattering by air molecules
- , which have direction-dependent optical properties, can produce polarized light through
Applications of polarization principles
- use polarizing filters to block glare from reflective surfaces
- The filters are oriented to absorb light, which is the main component of glare (water, snow, roads)
- Liquid Crystal Displays (LCDs) use polarizing filters and liquid crystal molecules to control light transmission
- Liquid crystal molecules change orientation in response to an applied electric field, altering the polarization of light passing through them
- This allows pixels to be turned on or off by controlling the transmission of polarized light (smartphones, computer monitors, televisions)
- in materials can rotate the plane of polarization of linearly polarized light
- Some materials, such as solutions of chiral molecules, exhibit this property (sugar solutions, amino acids, certain crystals)
- The angle of rotation depends on the material's specific optical rotatory power and the path length of light through the material (glucose concentration measurement in medical applications)
- uses polarized light to analyze stress distributions in transparent materials
Polarization and wave interactions
- principles apply to polarized waves, affecting their interference patterns
- describes the intensity of linearly polarized light transmitted through a polarizer as a function of the angle between the polarization axis and the polarizer axis
Key Terms to Review (30)
Anisotropic Materials: Anisotropic materials are substances that exhibit different physical properties, such as optical, electrical, or mechanical, along different directions. These materials lack the same properties in all directions, unlike isotropic materials which have uniform properties regardless of the direction.
Axis of a polarizing filter: The axis of a polarizing filter is the direction along which the filter allows light waves with specific orientations to pass through. It determines the plane of polarization for transmitted light.
Birefringence: Birefringence is the optical property of a material that causes it to have two different indices of refraction for light traveling in different directions. This phenomenon occurs in anisotropic materials, which have a varied structure and refractive properties depending on the direction of light. Birefringence is significant in understanding how materials interact with polarized light, affecting applications such as optics and imaging systems.
Birefringent: Birefringent materials have different refractive indices for light polarized in different directions. This causes the splitting of a light wave into two separate waves when it passes through such materials.
Birefringent Polarizers: Birefringent polarizers are optical devices that utilize the phenomenon of birefringence to polarize light. Birefringence is the ability of certain materials to split an unpolarized beam of light into two separate, polarized beams due to their anisotropic crystal structure.
Brewster’s angle: Brewster's angle is the angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface without any reflection. It occurs when the refracted and reflected light rays are perpendicular to each other.
Brewster's Angle: Brewster's angle, also known as the polarizing angle, is the angle at which light reflected from a surface is completely polarized in a direction perpendicular to the plane of incidence. This phenomenon is important in the study of polarization, a fundamental concept in optics and electromagnetism.
Brewster’s law: Brewster's law states that the angle at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection, is known as the Brewster angle. This occurs when the reflected and refracted light rays are perpendicular to each other.
Circular Polarization: Circular polarization is a type of polarization where the electric field of an electromagnetic wave rotates in a circular motion as the wave propagates. This rotation can be either clockwise (right-handed) or counterclockwise (left-handed), resulting in two distinct polarization states.
Dichroic Polarizers: Dichroic polarizers are a type of optical filter that selectively transmits light waves vibrating in one particular orientation while absorbing waves vibrating in the perpendicular orientation. This property of selectively transmitting and absorbing specific polarization states is known as dichroism, hence the name dichroic polarizers.
Direction of polarization: Direction of polarization refers to the orientation of the electric field vector in an electromagnetic wave. It describes how the electric field oscillates as the wave propagates.
Electromagnetic spectrum: The electromagnetic spectrum is the range of all types of electromagnetic radiation, which includes visible light, radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. This spectrum is crucial because it encompasses the various forms of energy that travel through space at the speed of light and affects many aspects of physics, including radiation, magnetism, wave production, and energy transfer.
Elliptical Polarization: Elliptical polarization is a type of polarization where the electric field vector of a transverse electromagnetic wave traces out an ellipse as it propagates. This is in contrast to linear polarization, where the electric field vector oscillates in a single plane, and circular polarization, where the electric field vector traces out a circle.
Horizontally polarized: Horizontally polarized light consists of waves in which the electric field vector oscillates parallel to the horizontal plane. It is a specific case of linearly polarized light.
Linear Polarization: Linear polarization is a type of polarization where the electric field of an electromagnetic wave oscillates in a single, fixed direction perpendicular to the direction of propagation. This contrasts with other forms of polarization, such as circular or elliptical polarization, where the electric field rotates around the direction of propagation.
Malus's Law: Malus's law, also known as the Malus law, is a fundamental principle in optics that describes the intensity of polarized light after passing through a polarizing filter. It governs the relationship between the intensity of the transmitted light and the angle between the polarization axis of the filter and the polarization direction of the incident light.
Optical Activity: Optical activity is the ability of certain molecules to rotate the plane of polarized light as it passes through a solution containing the molecules. This phenomenon is caused by the asymmetric arrangement of atoms within the molecular structure, which interacts with the electromagnetic waves of the light.
Optically active: Optically active substances rotate the plane of polarized light passing through them. This property is due to asymmetry in their molecular structure.
Photoelasticity: Photoelasticity is a property of materials that allows them to exhibit changes in optical properties when subjected to mechanical stress. This phenomenon is used to visualize stress distributions in transparent materials by observing the patterns of polarized light transmitted through them. It connects the behavior of light, particularly polarization, with the mechanical properties of materials, making it a valuable tool in stress analysis.
Polarization: Polarization is the process in which waves, such as light or electromagnetic waves, are restricted to vibrate in a particular direction. It also refers to the separation of charges within an object when exposed to an electric field.
Polarization: Polarization is a fundamental property of electromagnetic waves, including light, that describes the orientation of the electric field oscillations within the wave. It is a crucial concept that underlies many important phenomena in the fields of static electricity, electromagnetism, and optics.
Polarized: Polarized refers to the alignment of charges or waves in a specific orientation. In physics, it can describe electric fields within conductors or the orientation of light waves.
Polarizing Filters: Polarizing filters are optical devices that selectively transmit light waves oscillating in a particular orientation, while blocking light waves oscillating in other orientations. They are used to manipulate the polarization of light in various applications, such as photography, display technology, and scientific instrumentation.
Polaroid Sunglasses: Polaroid sunglasses are a type of eyewear that use a specialized lens coating to selectively filter and block certain polarized light waves, reducing glare and improving visual clarity in bright outdoor conditions. This technology is particularly useful for activities like driving, boating, and sports where glare can impair vision.
Rayleigh Scattering: Rayleigh scattering is a physical phenomenon in which light is scattered by particles much smaller than the wavelength of the light. This type of scattering is responsible for the blue color of the sky and the reddish appearance of the sun during sunrises and sunsets.
Reflected light is completely polarized: Reflected light is completely polarized when the electric field vectors of the reflected wave oscillate in a single plane perpendicular to the direction of propagation. This occurs at a specific angle of incidence known as Brewster's angle.
Transverse Waves: Transverse waves are a type of wave in which the oscillation of the medium is perpendicular to the direction of wave propagation. This distinguishes them from longitudinal waves, where the oscillation is parallel to the direction of wave travel. Transverse waves are an important concept in the study of waves, diffraction, and polarization.
Unpolarized: Unpolarized light consists of waves vibrating in multiple planes perpendicular to the direction of propagation. Common sources of unpolarized light include sunlight, incandescent bulbs, and fluorescent lights.
Vertically polarized: Vertically polarized light has its electric field oscillating in the vertical direction. This type of polarization is one of the simplest forms to analyze due to its well-defined orientation.
Wave Superposition: Wave superposition is the principle that describes how waves, such as sound waves or electromagnetic waves, combine when they encounter each other. It states that the displacement at a point is the sum of the displacements of the individual waves at that point.