Question

Determine the thickness in microns an antireflection coating for a slab of crown glass (n = 1.52) that is meant to be used at an angle of incidence of 45°. Use MgF2 (n = 1.37) as a coating material, design for a vacuum wavelength of 512 nm, and assume that the incident index is that of air.

Answer 1

Solution :

Refractive index of anti-reflective coating of Magnesium Floride, n₁ = 1.37
Refractive index of a slab of crown glass, n₂ = 1.52
Now, Let the thickness of the film be t.
Then,

where, = 512 nm

Now, the thickness of the film, t is given by the expression :

Therefore, the thickness is 93.43 nm, or the thickness is 0.09343 microns.