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Materials Science > Optical Properties > Flashcards

Optical Properties Flashcards

1
Q

what are transparent, translucent and opaque materials, respectively?

A

transparent: see through
translucent: let light through
opaque: doesn’t let any light through

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2
Q

what are optical properties?

A

a materials response to exposure to electromagnetic radiation especially to visible light

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3
Q

what are the 2 things light can behave as?

A

a particle or a wave

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4
Q

what is a photon

A

a quantum unit of light

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5
Q

what do the variable “E”, “v”, “h” and “c” represent respectively

A

energy of a photon, frequency, planck’s constant, speed of light in a vaccum

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6
Q

radiations are packets of energy known as what?

A

photons

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7
Q

if light is transmitted, what will happen to the electron cloud?

A

the cloud will distort in shape

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8
Q

which is greater, the velocity of light in a material or vacuum

A

vacuum

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9
Q

if we add large ions to glass, what happen to the speed of light through the glass

A

it will decrease

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10
Q

if phi(0)>phi(c), what is the case

A

light is totally internally reflected

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11
Q

how do you determine the critical angle

A

its when phi(2) is 90deg

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12
Q

why are fiber optic materials cladded in low n material

A

so that the light will be totally internally reflected

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13
Q

what can be said about the size of the distance between energy states in metals

A

its very small

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14
Q

what does the small size of the energy gap in metals mean in terms of absorption

A

it means almost any frequency of light can be absorbed by metals

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15
Q

true or false, almost all light coming into a metal is absorbed within 0.1 micrometers of the surface

A

true

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16
Q

what types of materials can electrons be absorbed by

A

metals and small band gap materials

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17
Q

what types of materials can nuclei be absorbed by

A

all

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18
Q

what is the energy lost in absorbtion light by metals lost as?

A

the remaining energy is lost as phonons

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19
Q

why are metals reflective

A

because the energy lost by a descending electron is the same as the incident one

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20
Q

when an electron transitions from excited state, what is emitted

A

a photon

21
Q

what does the color of reflected light depend on

A

the wavelength

22
Q

true or false, metals are more transparent to very high energy radiation, like X-rays and gamma-rays

A

true

23
Q

what can be said about an amorphous polymer in terms of scattering of light

A

very little to no scattering

24
Q

If a polymer is transparent, what can be said about its strucutre

A

it will be an amorphous polymer

25
Q

what can be said about an semi-crystalline polymer in terms of scattering of light

A

they scatter light a little

26
Q

where does scattering of light occurs

A

at boundaries

27
Q

highly crystalline polymers will be what

A

opaque

28
Q

if a polymer goes from being amorphous to drawn what can be said about its optical properties

A

it becoming increasing crystalline, therefore it will become increasingly opaque

29
Q

for non-metals, what has to be the case for light to be absorbed

A

hv

30
Q

if a semiconductor appears as metallic, what does this mean?

A

the visible photons were all reflected

31
Q

what it the relationship between the impurities and the aborption

A

more impurities=more absorption

32
Q

how does an increase in impurities cause an increase in absorbtion

A

impurities divide up the band gap to allow transitions with less energy than Egap

33
Q

how is the color of nonmetals determined

A

by the sum of the frequencies of the 1. transmitted light and 2. the remitted light from the electron transitions

34
Q

how can an image become blurred

A

if the transmitted light is scattered internally

35
Q

what are 3 factors that cause scattering?

A
  1. grain boundaries
  2. pores in ceramics
  3. different phases in materials
36
Q

what is luminescence

A

the reemission of light by a material. material absorbs light at one frequency and reemits it as another

37
Q

how is phosphorescence achieved

A

if the resting time in the trapped state is relatively long (>10^-8 seconds)

38
Q

what is photo luminescence?

A

as electrons fall back to their ground states, UV light is emitted

39
Q

how are colored lamps made?

A

by lining the inside of the tube with a material that only absorbs UV and re-emits visible light

40
Q

how can we dictate the color of these “colored lamps”

A

by doping with various metal cations

41
Q

what is cathodoluminescense

A
  • the inside of a tube is coated with a phosphor material.
  • the phosphur is bombarded with electrons
  • the electrons in phospur are excited to higher levels
  • visible light is emitted as electrons drop to lower ground states
42
Q

what does the color of light depend on in cathodoluminescense

A

the composition of the phoshur

43
Q

what can be said about the direction of the light that is emitted in cathodoluminescense

A

its random in phase and direction

44
Q

how is total internal refraction made possible in fiber optic cables

A

by a specific difference in the indicies of refraction of the cladding and the core

45
Q

what is the problem with the step index design

A

the different light rays travel different distances and reach the end at different times, limiting data communication

46
Q

what design of index was created to rectify the problem

A

the graded-index

47
Q

how is this design achieved

A

by parabolic doping

48
Q

how does the graded-index design fix the problem

A

becuase the rays travelling in the outer regions are going through lesser indicies of refraction therefore they travel faster (according to V=C/n), making them arrive at the same time

49
Q

if the emitted light has the same energy and phase as the incident light, what is this called

A

coherent

Materials Science (13 decks)

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