Optics III final L4: Polarization and Scattering

at Brewster's angle, which component is present?

Es, Ep goes to 0

what do Es and Ep stand for?

Es= parallel component (Rs= reflectance of the Es component) Ep= perpendicular component (Rp= reflectance of the Ep component)

perpendicular incidence follows what law

Fresnels law of reflection

what is the formula that relates Intensity to wavelength

I= 1/ lambda to the 4th

what is the rule for unpolarized light starting with 100 units incident?

If 100 units of light pass through a linear polarizer, 50 units of light leave, which will be polarized along the transmission axis of the polarizer.

scatter from cataracts is due to what 2 properties?

Mie and Coherence scattering

corneal haze following PRK is due to what 2 properties?

Mie scattering and coherence scattering

T/F: one of the main reasons we model light as a transverse wave is so that we can use the model to explain polarization

True

T/F: When the transmission axis of the polarizer is vertical, reflections from both car windshields and lights off the floor are minimized

True! these have a horizontal polarization so vertical polarizer minimizes it

what are 3 ways to generate polarized light?

1) pass unpolarized light through a special filter 2) reflecting unpolarized light off an APPROPRIATELY tilted surface (ex. light unpolarized from sun, but after reflecting off a lake, becomes polarized) 3) scattering the unpolarized light in a specific direction -ex. birefringence with calcite and anisotropic natures ***NOT sending unpolarized light through a lens (will still come out unpolarized)

what 3 things is scattering dependent on

1) size of the particles (small, inhomogeneities) 2) distance between particles 3) strength of interaction between light and the particles (the n and A values)

as the angle of incidence increases, what 2 things also increase?

1) the amount of light with polarization parallel to the surface increases 2) the amount of light with pol. perpendicular to the surface decreases to 0 (at Brewster's angle), and then increases again **thing about the graph these are the 2 components E(perpendicular) and Es(parallel)

In the case of polarization by scattering for unpolarized light incident, light will go off in all directions EXCEPT it will be in 1 direction:

1) vertically: with horizontal polarization 2) horizontally: with vertical polarization

at a 90 degree angle of incidence, both Ep and Es are...

100%

When vertically polarized light is incident upon a single linear polarizer with a vertical transmission axis, what percentage of the light will be transmitted?

100% -parallel to the incident polarization does not block out any of the light

When vertically polarized light is incident upon a single linear polarizer with a transmission axis at 45 degrees, what is the orientation of the polarization of the transmitted light?

45 degrees parallel to the transmission axis

Which of the following will not select one component of the polarization? 1) Unpolarized light passing through a specially designed filter 2) Reflecting unpolarized light off an appropriately tilted surface 3) Scattering unpolarized light in a specific direction from small particles 4) Sending unpolarized light through a lens

4: unpolarized light through a lens will still be in all directions out of the lens

When unpolarized light is incident upon a single linear polarizer with a horizontal OR vertical transmission axis, what percentage of the light will be transmitted?

50%

When vertically polarized light is incident upon a single linear polarizer with a transmission axis at 45 degrees, what percentage of the light will be transmitted?

50%

larger particles that have Mie scattering cause what scatter direction? what vision problems are associated?

backwards, cause fundus imaging issues

what is another clinical application of polarized light?

binocular vision tests stereopsis

mechanical stress can produce what

birefringence

What is birefringence? what material exhibits it

calcite -leads to a double image via double refraction and 2 separate n values within the same material -the light associated with each image is plane-polarized-perpendicular to the other

what does anisotropic mean?

calcite: a material has different structure (n's) in different directions -bc indexes of refraction are different, the wavelengths are also different (can produce phase changes)

LCD screens involve what type of polarizer

circular

shifting a polarization wave by 90 degrees results in (quarterwave plate)

circular polarization

for rayleigh scattering, light intensity increases as wavelength ___

decreases

circular polarizers are directionally ____

dependent (rotational dependency), but overall independent of random tilts bc clockwise is still percieved as clockwise, etc -unpolarized light passing backwards remains unpolarized as it passes through the quarterwave plate, then gets plane polarized

what do we need to do to create a polarizer?

design a material that only allows oscillation of molecules in a single direction -the electrons will only oscillate in 1 direction and ONLY that direction of orientation for the polarization will be absorbed

what does circular polarization help us analyze clinically?

disc hyperpigmentation --> independent of random tilts -glaucoma

at an angle of 0 degrees, Ep and Es are___

equal

T/F: All LCD/LED displays had an orientation where a linear polarizer would block all or most of the light

false, most of these were circularly polarized

smaller particles that have Mie scattering cause what direction of scatter? what vision problems can this cause

forward, can cause glare

unpolarized light tends to follow the rule that:

half the light hitting a polarizer will pass through along the SAME transmission axis of the polarizer

According to polarization by scattering, if vertical light is incident, what 2 outcomes are possible?

horizontal or diagonal polarization -the vertically incident light will get polarized (there is no vertical scattering)

reflections from flat surfaces are ______ polarized

horizontally, minimized by a vertical transmission axis

if a problem has unpolarized light passing through 2 filters with a 35 degree trans axis and it is assumed to be ideal, how would u find the amount of light that passes through (%)

ideal means that exactly 50% of the incident light gets through -so you would do .5cos squared 35 degrees x100 percent

what are the units of polarization

intensity in units (photons)

what is an application of tyndall scattering

iris light blue eye color -the blue color is due to tyndall scattering in the transluencent layer of the iris (in absence of melanin, the layer is translucent, and the light passing through undergoes tyndall scattering (random and diffuse scattering, it also takes place to a greater extent at shorter wavelengths (blue-green)

what is the basis of polarization by scattering?

light coming in gets scattered in a certain direction by small particles ex. light incident is scattered off vertically, it will be horizontally polarized (we need a vertical polarizer to minimize) ex 2. light incident is scattered off horizontally, it will be vertically polarized (we need horizontal polarizer to minimize)

what is one example whereby polarized light was generated?

lining up an array of thin vertical wires: made the electrons oscillate in one direction, component of polarization that was PERPENDICULAR gets transmitted -creates a vertical polarizer with a vertical transmission axis

what are the 2 rays of birefringent materials? what are some more examples of them?

no and ne (ordinary and extraordinary) -calcite, quartz, sodium nitrate, ice

until brewsters angle, more light reflects in which direction?

parallel than perpendicular **parallel to the surface reflects more

what is multiple scattering?

reduces wavelength dependence overall

what are the 4 options when light interacts with matter

reflects, absorbs, transmits, scatters

explain a specific case where adding a filter could actually increase the amount of transmitted light?

say you have unpolarized light--> vertical filter--> horizontal filter, if you add a 45 degree filter in between the vertical and horizontal, you would increase the amount transmitted from 0 to about half ish

what is resonance radiation?

scattering from the absorbers themselves

describe rayleigh scattering, what is the main contributor, intensity is stronger for what wavelengths

size is less than 1/10 wavelength -main contributor is dipole re-radiation -uniform in all directions (bc so small), and intensity is stronger overall for shorter wavelengths (appear bluish)

for polarized light, the electric vector oscillates in a ___

specific direction -ex. vertically oscillates (up and down) -ex. horizontally oscillates (R to L)

what is a halfwave plate

starts in phase and leaves out of phase by 1/2 wavelength (180 degrees oop)

what is a quarterwave plate?

starts in phase, leaves oop by 90 degrees of 1/4 wavelength--> creates circular polarization

light passing through a thick NFL layer will produce; through a weak NFL layer?

strong polarization and phase change weak polarization and small phase change

How do polarized sunglasses work?

surfaces we look at are horizontally polarized, so having glasses that only transmit the light vertically (vertical transmission axis) will minimize the light/glare and haziness

What is Brewster's angle?

tan inverse (n2/n1)

what component reflects the most amount of light?

the Es component (parallel), also polarizes all the light (it never decreases)

polarization is used to measure changes in what

the RNFL in glaucoma

with a horizontal surface, a horizontal transmission axis would get rid of which component?

the Rp component, all of the light would go through Rs curve

polarized light tends to follow the rule that:

the amount of light leaving a polarizer depends on the difference of orientation of the filter and polarization : aka Malus's law (can calculate the amount leaving) ex. vertical polarized incident light with a vertical polarizing filter: 100% goes through ex. horizontal polarized light going through a vertical: 0% goes through (directly orthogonal)

what is Brewster's angle

the angle for which only the s-component of polarization is reflected (100% of light is parallel to the surface) -p component is completely eliminated (no light exists that is perpendicular to the surface)

what is a polarizer's transmission axis defined as?

the axis parallel to the polarization that is transmitted (in other words, the one opposite is the one that blocks/minimizes it)

what property dictates how much light of a certain polarization gets absorbed?

the ease with which the electrons can oscillate in a specific direction (similar to an affinity)

why do sunsets appear red?

the long path of the atmosphere at sunset completely scatters away the shorter wavelengths of light (the blue light) -also rayleigh scattering!! -only redish tints reach our eyes (the longer wavelengths)

describe Tyndall scattering, it is dependent or independent of factors, what are examples

the particle size is about the same as the wavelength -impacted by wavelength effects inside the particle (like diffraction/resonances) -is spread out in 1 direction, is wavelength dependent and sensitive to particle size as well (SENSITIVE TO BOTH) -ex: halos seen through a fogged car window

describe Mie scattering, is it dependent/independent of things, what are examples

the particle size is much larger than the wavelength -strongly peaks in the forward direction and are wavelength INDEPENDENT -produces UNpolarized scattered light ex. fog and clouds, sky -this is why clouds look white/gray Mie scattering color will always look white/gray/black

in terms of polarization by reflection, as the angle of incidence changes, the amount of reflected light depends on what

the polarization

the orientation of the emergent light is always _____ the transmission axis of the polarizing filter preceeding it

the same as

what is the rule for polarized light?

the transmitted intensity always lies along the transmission axis of the polarizer and is proportional to malus's law

the linear polarization pattern describes a wave in what direction?

transverse wave, with the displacement perpendicular to the direction of travel

what is the most important scattering for the human eye?

tyndall scattering

normal light is ____ bc the nature of oscillations in the natural environment is ___

unpolarized (made up of components of every possible polarization); they are oriented randomly and not in 1 specific direction over another

Normal light (most of what you encounter on a daily basis: the sun, incandescent bulbs, etc...) is what

unpolarized (normal white light) made up of components of light from all different directions and polarizations

the majority of light is ___, what are some examples?

unpolarized; sun, lamps, candlelight

any diagonal polarization can be expressed as a sum of what 2 components

vertical and horizontal -can find the Intensity of each component I=A squared Ix= A2 cos2theta Iy= A2 sin2theta

what about is horizontal light is incident, what polarizations are possible?

vertical or diagonal -the horizontal incident light gets polarized, there is no horizontal scatter possible

if you send unpolarized light through a long series of filters (ex. horizontal, then 15 degrees, then 30 degrees, then 60 degrees, and finally vertical) what will be the orientation of the polarization leaving the last filter?

vertical!! for unpolarized, only depends on the orientation of the last filter

what are some directions of polarization

vertical, horizontal, diagonal, circular/elliptical

what is coherent scattering? clinical examples?

when particles are closer together than the coherence length, constructive and destructive interference occurs b/t the waves ex. corneal edema (scattering from the collagen fibrils), cataracts (proteins in the lens clump together and scatter the light-> cloudiness) ***both of these are also due to Mie scattering

what are the 3 categories for particle size?

1) particles are larger than the wavelength size (Mie scattering) 2) same size as the wavelength (tyndall scattering) 3) smaller than the wavelength (rayleigh scattering) -all are transparent, weak absorbers

a 90 degree difference in filters in series, for both unpolarized and polarized light, will result in how much light leaving the system?

0 units!!! ex. unpolarized--> vertical--> horizontal= 0 out

When vertically polarized light is incident upon a single linear polarizer with a horizontal transmission axis, what percentage of the light will be transmitted?

0% -this is minimum polarization perpendicular to the incident polarization

with a horizontal surface, a vertical transmission axis would get rid of which component?

Rs component, would leave the perpendicular Rp component

Describe the trends of the 2 components Rs and Rp as the angle increases from 0

Rs: increases gradually towards brewsters angle, then spikes up after it Rp: decreases initially, goes to 0% exactly at Brewsters angle, then sharply increases after

why is the sky blue?

The air molecules scatter blue light better than red light, so more blue light reaches our eyes. ---> rayleigh scattering!!! -the scattering intensity is stronger for shorter wavelengths (blue light) than for longer wavelengths