A thin layer of magnesium fluoride (n=1.39) is deposited on a layer of glass (n=1.52).?

A thin layer of magnesium fluoride (n=1.39) is deposited on a layer of glass (n=1.52).


a. Find the speed of light in the magnesium fluoride and the glass.


b. Light with a wavelength of 400nm in a vacuum is reflected from the coating. What is the minimum thickness of the coating?A thin layer of magnesium fluoride (n=1.39) is deposited on a layer of glass (n=1.52).?
a) assuming:


n = v air / v film





Where n = refractive index of the film


v = speed of the light wave





v film = v air / n


v film = 3E8 / 1.39


v film = 2.16 E8





b) L (lambda...) = 400nm I'm not so sure about this one. You have to find the wavelength in the coating, which would be lambda/n:


400nm/1.39, and that's what we need to consider...





You want a coating thickness that results in a 2-way light path that produces a phase reversal between the first- and second-surface reflections.





But when light reflects from the boundary of a transition from low n to high n, the reflection itself produces a phase reversal. So for the n=1.39 coating, there is a reflection phase reversal and the 2-way path must produce an integer number wavelengths phase shift.





Yikes, is this ever easier with a diagram... are you good from here?