Antireflective Coating

Question 1

What is used to measure the thickness of the tear film

Answer 1

Interference fringe

Question 2

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

Answer 2

Anti reflective

Question 3

How much light is lost by a spectacle lens?

Answer 3

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)

Question 4

How does antireflective film on glass work?

Answer 4

Front and back surface reflections destructively interfere

Question 5

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

Answer 5

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)

Question 6

What is the ideal coating for antireflective?

Answer 6

Magnesium fluoride

Question 7

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

Answer 7

Thickness

Question 8

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

Answer 8

A quarter of the wavelength in the thin film

tn=lambda/4

Question 9

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

Answer 9

The optical thickness

Question 10

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

Answer 10

4.3% to 1.5%

Question 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?

Answer 11

Use t=lambda/4n

100nm

Question 12

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

Answer 12

Multilayer coating

Question 13

Percentage of light through an uncharted surface?

Answer 13

4.3%

Question 14

Percentage of light through single coating on a surface

Answer 14

1.3%

Question 15

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

Answer 15

0.5%

Question 16

Advantages of anti reflection to patients

Answer 16

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

Question 17

Disadvantages of AR coating

Answer 17

• exaggerated appearance of dirt

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

Question 18

What is the solution to the cosmetically unattractive dead grey

Answer 18

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

Question 19

Interference filter

Answer 19

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

Question 20

Types of filters

Answer 20

• long pass interference filters
• short pass interference filters
• band pass interference filters

Question 21

Long pass interference filter

Answer 21

Only permits longer wavelengths to pass through

Question 22

Short pass interference filters

Answer 22

Only permit shorter wavelengths to pass through

Question 23

Band pass interference filters

Answer 23

Only permit a certain wavelength band to pass through

Question 24

Hot mirror

Answer 24

Reflect IR and transmit visible

Question 25

Cold mirror

Answer 25

Reflect visible and transmit IR

Question 26

Biological mirror that reflects light which passes through rods and cones

Answer 26

Tapetum lucidum

Question 27

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

Answer 27

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

Question 28

Tapetum increases the sensitivity of the cats vision by ____

Answer 28

44%

Question 29

How does tapetum lucidum act to increase retinal sensitivity

Answer 29

By reflecting light back through the photoreceptors layer

Question 30

Which is commonly used single layer anti reflection coating material

Answer 30

Magnesium fluoride

Question 31

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

Answer 31

1.5%

Question 32

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

Answer 32

0.5%

Question 33

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

Answer 33

Quarter