Part A (4 pts) Consider light of wavelength λ = 670nm traveling in air. The light is incident at normal incidence upon a thin film of oil with n2 = 1.75. On the other side of the thin film is glass with n3 = 1.5. What is the minimum non-zero value of the film thickness d that will cause the reflections from both sides of the film to interfere constructively?

On both sides of the film, the mediums have lower refractive index.

for interfering pattern from above, for constructive interference of reflected wave from both sides of the film, the condition is

2μt = (2n + 1) λ / 2

μ is refractive index of film, t is thickness of film λ is wavelength of light

n is order of fringe

for minimum thickness

n = 0

2μt = λ / 2

t = λ / 4μ

= 670 / 1.75 x 4

= 95.71 nm.