Question

Light of wavelength λ travels through a medium with an index of refraction n1before striking a thin film with an index of refraction n2 at an angle of incidence of 0. Some of the light is reflected off of and some is transmitted through the n2 thin film. The transmitted light travels a distance t through the thin film before encountering the n1 medium again. Some of the light reflects off of the n1 medium.

What is the effective path length difference between the light that reflected off of the n2 medium and the light that reflected off the n1 medium, given that n1>n2?

A. t+λ/n2

B. 2t+λ/n2

C. 2t+λ/(2n2)

D. t+λ/(2n2)

Answer 1

Option C is correct.

Light that transmits through n2, travels t distance before reflection off the n1 medium and again travels distance t before reaching the point from where it entered n2 medium. Hence it travels 2t distance more than the light that is reflected off n2.

It( light entering n2) also travels an additional distance equal to , half of wave length, when reflected off n1 ( as n1 is greater than n2). Wavelength in n2 is /n2.

Hence path length difference = 2t + /2 n2

answered by: anonymous