Polarization II Flashcards
The blue light is __________ for light coming from the points in the sky 90 degrees away from the sun
Linearly polarized (rayleigh)
The light coming from directions near the sun or opposite the sun is _________
Unpolarized (Mie)
For regions in between 90 away from the sun and around the sun, the light is ________
Partially polarized (tyndall)
Waggle dance of the bee shows not only the ________ of he food, but also the __________ of the food location
Direction
Distance
What is the purpose of the tail waggling dance of a bee?
To communicate the direction of food to the other bees relative to the position of the sun
What is a requirement for a correct waggle dance for a bee
Must be able to read the suns postion from the blue sky.
Photoreceptors of the bees compound eyes
Exhibit a strong sensitivity to polarized light
Bees have a ___________ in the medulla, suggesting that polarization patterns in the sky may be analyzed by the brain
Polarization sensitive neuron
When one views objects through a properly oriented transparent, polished calcite crystal, the image is doubled. This phenomenon is known as __________________
-birefringence or double refraction
The light associated with each image is ________________ to that of the other ( in birefringence)
Plane-polarized perpendicular
The material of a birefringent object
Has different structure in different directions (anisotropic)
For incident frequency, crystal (anisotropic medium) is _________ for both the horizontally and vertically polarized light
Transparent
The ______________ are different for the two polarizations. This difference in refractive index leads to the birefringence or double refraction phenomenon
Refractive indices
When light propagates down the internal optical axis crystal, the different polarization components travel at ______________ due to the different indices of refraction
Different speeds
What happens when a light passes through a refractive index?
- wavelength changes
- speed changes
- frequency does not
What remains constant when light passes through a refractive index?
Frequency
The polarization component perpendicular to the plane of the paper behaves as expected and the associated ray is called the _________
Ordinary or o-ray
The polarization component represented by the double arrows does not behave as expected, instead it moves diagonally upward as it propagates through the crystal. The ray associated with this component is labeled ______
The extraordinary or e-ray
A crystal that transmits one component and absorbs the other
Dichrotic
The property by certain materials having different absorption coefficients for light polarized in different directions
Dichroism
What is intrinsic dichroism based on?
Specific absorption properties of the materials
What is form dichroism based on?
Specific structure of the materials (calcide crystal)
Birefringence is introduced by ________ of a material
Anisotropy
What does the anisotropy of a material depend on?
The refractive index of the material depends on the direction of light propagation and on the polarization state of the light
Birefringence in biological tissue
Anisotropy is often generated by a compounding of at least two homogenous dielectric materials
How do you observe measurable birefringence in biological material
Materials have to be arranged in an organized manner
Fibrils that are surrounded by material of different refractive index
Birefringence of a organized manner is called
Form birefringence
When light traverses a birefringent materials, a relative delay between two orthogonal polarization states is introduced that accumulates with thickness of the material. This delay is known as
Phase retardation
Creates 90 degree phase shift. Converts linear polarization into circular polarization
Quarter wave plate
Difference in optical path length
(N slow-n fast)d = optical path difference
This is what produces birefringence
Rotates a linear polarization by 90
Half wave plate
Very small changes in refractive index can do what to polarization
Create very large changes in polarization that can be easily visualized with a polariscope
In the normal eye, polarization specific retardation of light occurs mainly in the ________, which contributes about _______ of the birefringence of the eye
Cornea
80%
Where does the remaining birefringence of the eye after the cornea originate from?
Retinal nerve fiber layers and Henle fibers of the central macula
The crystalline lens, tear film, aqueous humor and vitreous and birefringence
Insignificant amount to the total ocular birefringence
Due to birefringence of cornea and lens, the state of polarization changes from linear to ___________
Elliptical
What causes more retardation partial polarization in the eye
Scattering of the fundus
Reflected polarized light in the eye
Affected again on this way back before exiting the eye
Birefringent property of cornea are due to its special structure ____________ called ‘stroma’
Form birefringence
How much of the cornea does the stroma make up?
9/10 of the thickness of the cornea
Retardation in the cornea will increase with what?
Angle of incidence
If light is incident parallel to the surface of the cornea, there is no _______
Retardation
When light hits the cornea at an eccentric angle of incidence this will cause _________
Retardation
What surface of the cornea is birefringence greater?
Anterior surface
What could alter the corneal birefringence
- IOP
- higher astigmatism
- corneal asymmetry
- post op corneal distortion
What does the maltese cross appearance come from in the cornea
Results from the regular arrangement of collagen lamellar in the cornea, which are birefringent
What is the birefringent property of the crystalline lens due to?
Form birefringence
Total birefringence of the lens
Negligible compared to in cornea by a factor of 10
Exhibits from birefringence due to the radially arranged nerve fiber layer of henle
Haidenger’s brush
Why does the birefringent nerve fibers of the macula act like a yellow radial polarizing filter
Fiber layer of henle which lies over the rods and cones of the macular region
Haidenger’s brush apparatus
Consists of a blue filter and a rotating linear polaroid placed over a light bulb
What is the haidenger’s brush apparatus used for?
Used to detect, diagnose, and train amblyopia due to eccentric fixation
Disruption or absence of a bow tie on the macula in fundus photo
Indicate severe damage to the photoreceptors, consistent with the finding of poorer visual acuity
When could patients perceive haidenger’s brushes?
When the proportion of polarized light reached 56 percent, although some could see them in only 25 percent polarized light
An ability to measure and test a persons ability to perceive polarization could potentially offer what
A simple and affordable screen for AMD
The study of how humans perceive polarization showed that your ______ can dramatically affect how you perceive polarized light
Cornea
Tool used to qualitatively assess birefringence of a material
Polariscope
The poalriscope is used to _______________
Assess birefringence in materials
Visualization of birefringence using a polariscope provides information about
- Lens material and how processed
- Stress on the lens
- The likely locations at which line fractures may occur if the lens is dropped or bumped
Localized birefringence indicates a weak point in the lens, which if significant should be replaced
