Question

Problem 9: Suppose you have a lens system that is to be used primarily for 680 nm red light. What is the second thinnest coating of magnesium fluorite, which has an index of refraction of n = 1.38, that would be non-reflective for this wavelength? Assume the index of refraction of the lens is bigger than 1.38, and enter your answer in nanometers. Numeric A numeric value is expected and not an expression.

Answer 1

The Condition for destructive interference

2nt = (m + 5)

Where m=0,1,2,----

For Second thinnest m=1

=>2*1.38*t = [1 + (1/2)] *(680*10^-9)

t =(1.02*10^-6)/2.76

t = 369.6 nm