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Optics 4 > Scattering > Flashcards

Scattering Flashcards

1
Q

scattering of light is due to the what in a medium?

A
  • in homogeneities

- particles

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2
Q

what are teh two conditions for incoherent scattering?

A
  1. need white or polychormatic light

2. particles must be far apart (greater than the coherence length)

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3
Q

incoherent scattering depends on what three things?

A
  1. size of the particles
  2. distance between the particles
  3. strength of the interaction
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4
Q

the strength of the interaction depends on what two things?

A
  1. refractive index

2. absorption strength

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5
Q

when does Rayleigh scattering occur?

A

when particles are SMALLER than the wavelength of light (smaller than like 500nm)
-dipole re-radiation

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6
Q

does rayleigh scattering go forward or backward?

A

both (in all directions)

-isotropic

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7
Q

rayleigh scattering has strong ____________ dependence

A

wavelength

-stronger dependence at shorter wavelengths

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8
Q

which wavelength, shorter or longer, scatters more for rayleigh scattering?

A

-short wavelength (blue) scatters MORE than long wavelength (red)

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9
Q

what is elastic scattering?

A
  • scattered photons’ energy DO NOT CHANGE

- rayleigh scattering

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10
Q

what is inelastic scattering?

A
  • loss of energy

- raman scattering

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11
Q

for rayleigh scattering, the intensity of scattering blue light is how much greater than the scattering of red light?

A

3.3 times greater

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12
Q

blue light effects what for humans?

A
  • effects melatonin levels

- effects the day night cycle

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13
Q

when does Mie scattering occur?

A
  • when particles are LARGER than the wavelength of light

- reflection and refraction

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14
Q

is mie scattering wavelength dependent?

A

nope

-wavelength INDEPENDENT

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15
Q

what direction does Mie scattering occur?

A

stronger forward scattering

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16
Q

Which scattering does absorption and scattering?

A

Mie

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17
Q

the smoke that comes off of a cig is blue, the smoke exhaled when smoking is white, why?

A
  • blue due to rayleigh scattering

- white because of moisture particles and Mie scattering

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18
Q

when does tyndall scattering occur?

A
  • when particles are EQUAL to the wavelength of light

- diffraction

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19
Q

is tyndall scattering wavelength dependent?

A

-yes! mostly…

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20
Q

what direction is tyndall scattering?

A

-scattering in many directions

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21
Q

a blue iris is due to what kind of scattering? iris lacks what?

A
  • tyndall scattering
  • lacks melanin
  • back scattering off of stroma
  • takes place at shorter wavelengths, so thats why blue
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22
Q

when the sun is shining, what parts of the sky show mie scattering and what parts show rayleight

A

mie: near the sun, sky looks whiter and weakly polarized
Rayleigh: over your head looking straight up, sky is deep blue and strongly polarized

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23
Q

when do you see a green flash as sunset?

A
  • refraction as light enters atmosphere
  • atmosphere is dispersive so green and blue have an optical path to observer
  • blue light is scattered more, so green is what is visible for us
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24
Q

what is said to happen for anyone who sees a green flash>

A

they will never make a misstep in matters of the heart

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25
Q

what is coherent scattering?

A
  • when particles are MUCH CLOSER TOGETHER than the coherence length of light
  • constructive and destructive interference occurs
  • particles are MUCH SMALLER than the wavelength of light
26
Q

coherent scattering acts as what

A

-diffraction grating

27
Q

waves in coherent scattering do what?

A

-propagate outward and overlap

28
Q

what two directions will coherent scattering waves interfere constructively?

A
  • parallel to incident light (forward scatter)

- refract relative to incident wave (phase shift)

29
Q

light scattering leads to what visual effects>

A
  • glare at night driving
  • facial recognition problems
  • haziness of vision
  • color and contrast loss
30
Q

for intraocular light scatter, what is FWS and what is BWS?

A

FWS: forward scatter, light going into the eye
BWS: backward scatter, light reflecting back from the fundus

31
Q

what tool do we use to asses the eye using backward scatter?

A

slit lamp

32
Q

why is the cornea transparent?

A

-parallel collagen fibrils that are less than the wavelength of light

33
Q

why would the cornea lose its transparency?

A
  • cant pump water out of the cornea
  • water builds up in lakes and they become large, 1/2 the wavelength of light
  • causes destructive interference
34
Q

how does a normal sclera work with scattering?

A
  • collagen fibers have a larger spacing that the wavelength of light
  • forward scattering, mie scattering, sclera is white
35
Q

scleral thinning?

A
  • fibers get smaller and become smaller than wavelengh of light
  • rayleigh scatting occurs, sclera becomes blue
36
Q

tell me about the crystalline lens and scattering

A
  • yellow pigments scatter more that light (forward)

- cataracts form when proteins build up and cause additional scattering

37
Q

tell me about vitreous humor and scattering

A
  • collagen fibers come together du to aging and cause LOCALIZED scattering
  • floaters
38
Q

retina and scattering?

A
  • retina scatters as much as the cornea (1/3)
  • disruption of blood circulation and build up of fluid increases scattering and turns area grey
  • backward scattering
39
Q

corneal transmittance is _________ dependent. what is their relation?

A
  • wavelength dependent

- as wavelength increases, transmittance increases

40
Q

what are the three characteristics of scattering that we know?

A
  • constant
  • wavelength dependent
  • can increase after refractive surgery
41
Q

who experiences more scatter, glasses or contact lens wearers?

A

CL wears by 0.22 log units

42
Q

what are the 3 common refractive surgeries that can result in increased scatter and name the type of scatter for each one.

A
  1. RK: increase stray light
  2. PRK: increase corneal backscattering
  3. LASIK: increase in stray light
43
Q

what is the 1 refractive surgery that results in DECREASED scatter post op?

A

corneal refractive therapy (corneal reshaping)

44
Q

what color eye will take longer to dilate and longer to return to normal?

A

brown

45
Q

what iris color has more scatter? why?

A
  • blue!

- lack melanin

46
Q

after the pupil reaches 3mm…

A

the pupil size dependence on scattering is weak.

-3mm is ideal

47
Q

for larger scatter angles and small pupils, scatter is dependent on what?

A

wavelength and pigmentation

48
Q

light scatter in the crystalline lens increases due to what?

A
  • age

- cataracts

49
Q

what are glistenings?

A
  • tiny baby water droplets

- water absorption and phase separation within the IOL material

50
Q

a monofocal IOL will have how much scattering compared to a normal 70 year old? 20 year old?

A

-less scattering than both!

51
Q

After surgery, is glistening a big deal?

A

YES! it increases like crazy! increases by 45% in a year!

52
Q

blue light blockers do what?

A
  • reduce the amount of blue light transmission in the eye
  • reduce light scatter
  • blocks harmful blue light from retina
  • reduces chromatic aberrations
  • DOES NOT EFFECT VA AND COLOR VISION
53
Q

what is a possible side effect of using blue light blockers?

A
  • decreased scotopic sensitivity

- worse eyesight in dim conditions

54
Q

the cornea experiences what kind of scattering?*

A
  • forward!

- constant!

55
Q

this iris contributes what to scattering?*

A
  • pigmentation

- diffuse transmission of red light

56
Q

the lens experiences what kind of scattering?*

A
  • forward scattering

- age and cataract dependent

57
Q

the vitreous humor experiences what kind of scattering?

A
  • forward scattering

- age dependent

58
Q

retina experiences what kind of scattering?

A
  • backward scattering!
  • pigmentation dependent
  • fundus reflectance of red light
59
Q

what is ciliary corona?

A

radiation of sharp needles of light that is perceived subjectively around a bright point source
-originates from light scattering by small particles

60
Q

what is lenticular halo?

A
  • colored band precieved surrounding a bright spot of light at a mean distance of 3 radius
  • only for larger pupils
  • eye lens fibers form a diffraction grating

Optics 4 (3 decks)

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