Antireflective Lenses Flashcards
For A/R coating to reduce reflections, an A/R coating must meet 2 conditions:
1) path condition - determines what the optical thickness of a single layer coating film must be
2) amplitude condition - amplitude of light waves in the lens material and the film must be equal
path condition:
film must be _ of wavelength thick or _ multiples of that
1/4, odd
path condition:
when light strikes the single layer coated lens surface, some light will reflect from _ and some from _
this causes _ phase, _ interference, and prevents reflections
coating surface
lens surface
out of, destructive
amplitude condition:
requires the amplitude of the light waves in the lens material and film to be _, creating _ interference
equal, destructive
amplitude condition:
index of film must be equal to _ of index of material being coated
square root
single layer coatings are not 100% effective because:
correct coating thickness for yellow waves is not correct for red or blue (blue and red are reflected more and form purple cast)
multilayer coatings (8 layers) work by:
adding more layers of coating, each specific to wavelength and increasing amount of light transmitted that would have normally been reflected
multilayer coatings are not placed directly on lens;
first _
then _
then _
primer
hardcoat
adhesion
when alternating layers of low and high index materials, it is possible to obtain reflectivity as low as _%
0.1
_ is primary material used for AR coatings as in Silica
Magnesium Fluoride (n=1.38)
AR is sealed with either _ or _ coating
hydrophobic or oleophobic
many new coatings are so efficient in repelling smudges, a temporary _ is applied to prevent slippage during edging
gripper coat
multilayer AR coatings are very important for _ lenses as they naturally transmit less light
high index
AR coatings are hard and brittle
plastic lenses are soft and spongy
-what supports brittle AR coating?
hardcoat
designing AR for the material that it will be placed upon is known as _
substrate matching
color that you can see on the lens is called
reflex color
multilayer coatings do not have purple cast; most today have _ appearance
blue-green
if lens has a reflex color that changes from one section of lens to another, it is an indication of _
even coating thickness
reflex color can be any color and still be effective; it also can have virtually _ and still be effective
no color
applying an AR coating _ a tinted lens;
therefore required to tint a lens _% darker than desired if AR is going to be applied
lightens
10-15
AR coating has what effect on sunglasses?
reduced mirror like reflections from back surface
pros of AR:
less reflections eyes more visible improved contrast less halos with night driving easier to clean/stays cleaner
cons of AR:
cost
smudges are more visible
AR coatings are _ fragile
thermally, chemically
