Polarization And Scattering Flashcards
What is the rule for unpolarized light?
half the light hitting a linear polarizer will pass through and the light leaving will be polarized along the transmission axis of the polarizer.
50% out
What is the rule for polarized light?
the amount of light leaving depends on the difference between the orientation of the polarization hitting the filter and the orientation of the filter’s transmission axis according to Malus Law
Describe the equation for Malus’s Law.
𝐼 = 𝐼0𝑐𝑜𝑠2𝜃
𝐼0 is the amount of light hitting the filter and 𝜃 is the angle between the polarization direction and the filter orientation.
The exiting light will be polarized along the transmission axis of the polarizer
What equation provides information for polarization by reflection?
Brewster’s angle
How can polarization be useful for glaucoma?
Used to measure changes in the RNFL in glaucoma (fibrous structure)
Compare a neutral density filter to a polarizer.
ND filter would get rid of part of the light causing dimmer reflections overall
Polarizers minimize one over the other
What is the goal of polarization in sunglasses?
Get rid of reflections hindering vision without limiting light needed to see.
When does polarization happen?
Whenever radiated energy or light comes from an excited molecule oscillating in one direction
Is natural light polarized?
No they are orientated randomly and tend to shift over time
Ex natural: sun
other examples: incandescent light, candlelight
What are three ways to generate polarized light?
- Pass unpolarized light through a specially
designed filter - Reflect unpolarized light off an appropriately tilted surface
- Scatter unpolarized light in a specific
direction from small particles (sun to eye depends on angle I am looking at sky and position of sun)
What are the directions of polarization? Does it affect the way our visual system perceives them?
Vertical, horizontal, diagonal, circular
No
What can any polarization be expressed as?
Sum of vertical and Horizontal Component (diagonal)
How can we create polarizers?
Design material that only allows oscillation of molecules in a single direction
How do we generate polarized light?
When light strikes a conducting material, free electrons absorb and begin to oscillate in one direction.
The component of polarization in the perpendicular will transmit.
What determines how much a polarizer can absorb?
The ease with which the electrons can oscillate in a specific direction once absorbed
When we have a series of polarizers how do we determine the orientation of light leaving the polarizer?
Follow the orientation of the last light leaving the filter
What happens when we have 2 polarizers one 90 and the other 180?
Crossed no light makes it though
Describe what occurs during polarization by reflection as the angle of incidence increases.
1) The amount of light with a polarization parallel to the surface increases
2) The amount of light with a polarization perpendicular to the surface decreases to zero (at a special angle called Brewster’s angle) and then it increases
At 90 degrees what percent reflectance are Rs and Rp?
100%
What direction is the polarization of polarized sunglasses?
Horizontally polarized
transmission vertical
Describe the relationship between polarization and scattering. Wavelength and scattering?
Scattered light is polarized
Short wavelength scatter more
Describe birefringence.
Leads to double image
2 different indices of refraction
The light associated with each image is plane-polarized perpendicular to that of the other
reason for the appearance of the double images is that the calcite crystal is anisotropic, which means the material has a different structure in different directions
What can cause birefringence?
Mechanical stress
Describe the phase retardation of a half wave, quarterwave, and full wave.
180 degree phase retardation
90 degree phase retardation
360 degree phase retardation
What makes up circular polarizers.
Linear Polaroid and quarterwave plate make a circular polarizer
How thickness affect circular polarization?
Thin- weak elliptical polarization
Thick- strong elliptical polarization
What create Haidinger’s Brush?
Polarization sensitive bundles
What 4 things can light do when it interacts with matter?
Scatter
Reflects
Transmits
Absorbs
What contributes to scatter?
Inhomogeneities (particles)
Scattering depends on size of particles, distance between, strength of interaction between light and the particles
What are.3 categories for particle size? What kind of scattering are they associated with?
Much larger than l (Mie scattering)
About the size of l (Tyndall scattering)
Much smaller than l (Rayleigh scattering)
Describe Mie scattering.
Much larger than wavelength
Transparent (weak absorber)
Forward direction
Wavelength dependent
Produces unpolarized scatter light
Ex: white light scatter, clouds
Describe Tyndall scattering.
About the size of wavelength
Transparent (weak absorber)
Scattering one direction
Wavelength dependent
Sensitive to particle size
Describe Rayleigh scattering.
Much smaller wavelength
Transparent (weak absorber)
Dipole re-radiation
Uniform in all directions
Stronger intensity for shorter wavelengths
Reflected light is perpendicular and polarized
Why is the sky blue? Why are sunsets red?
Rayleigh scattering
Blue light scatters off and we’re left with red
Why are blue eyes blue?
Tyndall scattering
How does multiple scattering affect wavelength dependence?
Reduces wavelength dependence
Describe coherent scattering?
Closer particles causes constructive and destructive interference occurs between the waves
Describe resonance radiation.
Scattering from the absorbers themselves
Describe the light from the sun.
Collimated
