What is antireflection coating? What should be the refractive index and minimum thickness of the coating?
When the light enters the optical instrument at the glass air interface, around 4% of light that too at single reflection is lost by reflection which is highly undesirable. In order to reduce the reflection loss, a transparent film of proper thickness is deposited on the surface. This film is known as antireflective coating.
Popular material used is MgF2 because of its refractive index is 1.38.
The minimum thickness of coating is given by: -
2nt = mλ
n = refractive index of film
t = thickness of film
m = 1, 2, 3, …
λ = light wavelength in vacuum (air)