Antireflective Coating Flashcards
What is used to measure the thickness of the tear film
Interference fringe
________ coatings on lenses are thin films that work according to the principles of interference
Anti reflective
How much light is lost by a spectacle lens?
- 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)
How does antireflective film on glass work?
Front and back surface reflections destructively interfere
How do you get destructive interference for the front and back of the lens?
- Reflections from film must travel a difference of lambda/2
- Ideal refractive index is 1.234 (for film), the best we can do is magnesium fluoride (1.38)
What is the ideal coating for antireflective?
Magnesium fluoride
With just the right _______ of a thin film, the second reflection interferes destructively with the first reflection
Thickness
The minimum thickness of an anti reflecting thin film on glass is
A quarter of the wavelength in the thin film
tn=lambda/4
The product of the thickness and the refractive index, tn2, is called
The optical thickness
Magnesium fluoride coating reduces the front surface reflection from ______ to ______
4.3% to 1.5%
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
A magnesium fluoride coating will reduce the reflection, but to reduce it further requires a _________
Multilayer coating
Percentage of light through an uncharted surface?
4.3%
Percentage of light through single coating on a surface
1.3%
Percentage of light getting through a multi coat film on single surface
0.5%