Question A6 It is desired to apply an anti-reflection coating on a glass lens used in air, by coating the lens with a thin film of magnesium fluoride of refractive index n = 1.37; (assume the glass has refractive index larger than nF). Write down the formula for optical path difference between waves reflected at top and bottom of the film, and use this to calculate the minimum required thickness of the coating to give a reflectance minimum for normal-incidence green light of wavelength 550 nm in air.

Question A6 It is desired to apply an anti-reflection coating on a glass lens used in air, by coating the lens with a thin film of magnesium fluoride of refractive index n = 1.37; (assume the glass has refractive index larger than nF). Write down the formula for optical path difference between waves reflected at top and bottom of the film, and use this to calculate the minimum required thickness of the coating to give a reflectance minimum for normal-incidence green light of wavelength 550 nm in air.