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Ophthalmic Optics > 13 - AR Coatings (Exam 3) > Flashcards

13 - AR Coatings (Exam 3) Flashcards

1
Q

When were AR coatings introduced and who originally used them?

A

1935 by Zeiss Optics

German military

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2
Q

What 2 conditions must an AR coating meet to reduce reflections?

A
  1. Path condition

2. Amplitude condition

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3
Q

What does the path condition determine?

A

Optical thickness a single layer coating must be

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4
Q

What does the amplitude condition require?

A

Amplitude of light waves in lens material and film are equal

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5
Q

How is the desired effect of the path condition reached?

A

Film must be an odd multiple of 1/4th the wavelength of a wave of light

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6
Q

What causes the path condition to reduce reflections?

A

Destructive interference

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7
Q

What causes destructive interference?

A

Waves being out of phase with one another

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8
Q

How does the amplitude condition relate to the path condition?

A

Ensures that the destructive interference caused by the path condition is complete

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9
Q

What must the index of the film be equal to so the amplitude condition is fulfilled?

A

Square root of the index of the material being coated

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10
Q

Why do single layer AR coatings have a purplish cast when viewed at certain angles?

A

Yellow light is reflected least

Blue and red are reflected most

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11
Q

What is a major benefit of multi-layer AR coated lenses?

A

Increased transmission

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12
Q

What is the order of layers going from the base lens to a multi-layer AR coating?

A 
Base layer
Primer
Hard coat
Adhesion Layer
AR
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13
Q

What are 2 primary materials used to fabricate AR coatings?

A
  1. Magnesium fluoride

2. Silica

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14
Q

What is the purpose of a gripper coat?

A

Prevents slippage during the edging of the lens

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15
Q

In what fashion are multiple layers of AR coating applied to a lens?

A

Alternating high and low refractive index

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16
Q

What is an AR coating typically sealed in by?

A

Hydrophobic top coat AND/OR

Oleophobic top coat

17
Q

How are hydrophobic lenses measured?

A

The angle they form with a drop of water on the surface (larger angle = more hydrophobic)

18
Q

For what type of lenses is multi-layer AR coating most important and why?

A

High-index lenses

They transmit less light

19
Q

What is the technique of design an AR coating for the material it will be place on?

A

Substrate matching

20
Q

If a lens does not have uniform reflex color across all sections, what does this indicate?

A

Unevenly applied AR coating thickness

21
Q

What is a challenge in creating an AR coating that has no reflex color?

A

Difficult to determine if the lens has an AR coating

22
Q

What is the result of applying an AR coating over a tint?

A

Lightens the tint

23
Q

What must you do to lens tint if you plan on applying an AR coat if you want to keep the desired tint?

A

Tint the lens 10-15% darker before applying AR

24
Q

What are 2 major cons to AR coated lenses?

A
  1. Cost

2. Smudges are more noticeable

25
Q

What 3 things should you avoid with AR coated lenses?

A
  1. Salt/bead warmers
  2. Caustic chemicals (acetone, ammonia, etc.)
  3. Dramatic temperature changes
26
Q

What does HEV do to perceived contrast and why?

A

Reduces contrast

Blue light scatters more easily than other visible light

27
Q

What can excessive blue light potentially cause?

A

Macular degeneration

28
Q

What cycle is altered by blue light exposure?

A

Circadian rhythm

29
Q

What are 4 benefits of blue light exposure?

A
  1. Boosts alertness
  2. Helps memory
  3. Increases cognitive function
  4. Elevates mood
30
Q

What is Essilor’s most abrasion resistant AR coat?

A

Crizal Sapphire

31
Q

What is Essilor’s AR coat that features HEV blocking?

A

Crizal Prevencia

Ophthalmic Optics (10 decks)

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