A thin oil film (n = 1.45) floats on water (n = 1.33) and is viewed from above in air under normal illumination with wavelength 600 nm in air. Only the reflection from the top surface of the oil film experiences a 180° phase shift. What is the least film thickness that results in no reflected light at this wavelength?
a) 300nm
b) 415nm
c) 210nm
d) 100nm