Antireflective Coating Flashcards Preview

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Flashcards in Antireflective Coating Deck (33):
1

What is used to measure the thickness of the tear film

Interference fringe

2

________ coatings on lenses are thin films that work according to the principles of interference

Anti reflective

3

How much light is lost by a spectacle lens?

8.4% of light incident on spectacle is lost. This reduces the illumination at the retina and is cosmetically unattractive. Light reflected into the eye by the back surface of the spectacle from the face is unwanted glare, especially at night
(4.2% for each surface)

4

How does antireflective film on glass work?

Front and back surface reflections destructively interfere

5

How do you get destructive interference for the front and back of the lens?

1. Reflections from film must travel a difference of lambda/2
2. Ideal refractive index is 1.234 (for film), the best we can do is magnesium fluoride (1.38)

6

What is the ideal coating for antireflective?

Magnesium fluoride

7

With just the right _______ of a thin film, the second reflection interferes destructively with the first reflection

Thickness

8

The minimum thickness of an anti reflecting thin film on glass is

A quarter of the wavelength in the thin film

tn=lambda/4

9

The product of the thickness and the refractive index, tn2, is called

The optical thickness

10

Magnesium fluoride coating reduces the front surface reflection from ______ to ______

4.3% to 1.5%

11

A MgFl (n-1.38) AR coating is placed on a glass lens. What is the minimum thickness of the film for incident light of wavelength 552nm?

Use t=lambda/4n
100nm

12

A magnesium fluoride coating will reduce the reflection, but to reduce it further requires a _________

Multilayer coating

13

Percentage of light through an uncharted surface?

4.3%

14

Percentage of light through single coating on a surface

1.3%

15

Percentage of light getting through a multi coat film on single surface

0.5%

16

Advantages of anti reflection to patients

-sees details more crisply
-environment appears brighter
-cosmetic benefit

17

Disadvantages of AR coating

-exaggerated appearance of dirt
-elimination of reflection by multilayer AR coating in not cosmetically beneficial (dead gray)

18

What is the solution to the cosmetically unattractive dead grey

Residual color allows some reflection that is cosmetically pleasing.
-bluish green, blue, gold color are preferred as residual colors

19

Interference filter

A high transmittance narrow band that transmits by constructive interference while reflecting all other wavelengths

20

Types of filters

-long pass interference filters
-short pass interference filters
-band pass interference filters

21

Long pass interference filter

Only permits longer wavelengths to pass through

22

Short pass interference filters

Only permit shorter wavelengths to pass through

23

Band pass interference filters

Only permit a certain wavelength band to pass through

24

Hot mirror

Reflect IR and transmit visible

25

Cold mirror

Reflect visible and transmit IR

26

Biological mirror that reflects light which passes through rods and cones

Tapetum lucidum

27

What is the difference between tapetum lucidum and AR coatings on specs?

OPL between reflections is lambda instead of lambda/2, thus constructive, rather than destructive interference occurs

28

Tapetum increases the sensitivity of the cats vision by ____

44%

29

How does tapetum lucidum act to increase retinal sensitivity

By reflecting light back through the photoreceptors layer

30

Which is commonly used single layer anti reflection coating material

Magnesium fluoride

31

Single layer anti reflection coating reduces light reflection from 4.3% to about ____

1.5%

32

How muc does a multi layer anti reflection thin film coating reduce the light reflection to about

0.5%

33

The minimum thickness of an antireflecting thin film on glass is ______ of the wavelength in the thin film

Quarter