Optics 4 > Scattering > Flashcards

Scattering Flashcards

(60 cards)

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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
what is coherent scattering?
- 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
coherent scattering acts as what
-diffraction grating
27
waves in coherent scattering do what?
-propagate outward and overlap
28
what two directions will coherent scattering waves interfere constructively?
- parallel to incident light (forward scatter) | - refract relative to incident wave (phase shift)
29
light scattering leads to what visual effects>
- glare at night driving - facial recognition problems - haziness of vision - color and contrast loss
30
for intraocular light scatter, what is FWS and what is BWS?
FWS: forward scatter, light going into the eye BWS: backward scatter, light reflecting back from the fundus
31
what tool do we use to asses the eye using backward scatter?
slit lamp
32
why is the cornea transparent?
-parallel collagen fibrils that are less than the wavelength of light
33
why would the cornea lose its transparency?
- 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
how does a normal sclera work with scattering?
- collagen fibers have a larger spacing that the wavelength of light - forward scattering, mie scattering, sclera is white
35
scleral thinning?
- fibers get smaller and become smaller than wavelengh of light - rayleigh scatting occurs, sclera becomes blue
36
tell me about the crystalline lens and scattering
- yellow pigments scatter more that light (forward) | - cataracts form when proteins build up and cause additional scattering
37
tell me about vitreous humor and scattering
- collagen fibers come together du to aging and cause LOCALIZED scattering - floaters
38
retina and scattering?
- 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
corneal transmittance is _________ dependent. what is their relation?
- wavelength dependent | - as wavelength increases, transmittance increases
40
what are the three characteristics of scattering that we know?
- constant - wavelength dependent - can increase after refractive surgery
41
who experiences more scatter, glasses or contact lens wearers?
CL wears by 0.22 log units
42
what are the 3 common refractive surgeries that can result in increased scatter and name the type of scatter for each one.
1. RK: increase stray light 2. PRK: increase corneal backscattering 3. LASIK: increase in stray light
43
what is the 1 refractive surgery that results in DECREASED scatter post op?
corneal refractive therapy (corneal reshaping)
44
what color eye will take longer to dilate and longer to return to normal?
brown
45
what iris color has more scatter? why?
- blue! | - lack melanin
46
after the pupil reaches 3mm...
the pupil size dependence on scattering is weak. | -3mm is ideal
47
for larger scatter angles and small pupils, scatter is dependent on what?
wavelength and pigmentation
48
light scatter in the crystalline lens increases due to what?
- age | - cataracts
49
what are glistenings?
- tiny baby water droplets | - water absorption and phase separation within the IOL material
50
a monofocal IOL will have how much scattering compared to a normal 70 year old? 20 year old?
-less scattering than both!
51
After surgery, is glistening a big deal?
YES! it increases like crazy! increases by 45% in a year!
52
blue light blockers do what?
- 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
what is a possible side effect of using blue light blockers?
- decreased scotopic sensitivity | - worse eyesight in dim conditions
54
the cornea experiences what kind of scattering?*
- forward! | - constant!
55
this iris contributes what to scattering?*
- pigmentation | - diffuse transmission of red light
56
the lens experiences what kind of scattering?*
- forward scattering | - age and cataract dependent
57
the vitreous humor experiences what kind of scattering?
- forward scattering | - age dependent
58
retina experiences what kind of scattering?
- backward scattering! - pigmentation dependent - fundus reflectance of red light
59
what is ciliary corona?
radiation of sharp needles of light that is perceived subjectively around a bright point source -originates from light scattering by small particles
60
what is lenticular halo?
- 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
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