We wish to coat flat glass (n = 1.50) with a transparent material (n = 1.20) so that reflection of light at wavelength 529 nm is eliminated by interference. what minimum thickness can the coating have to do this?

For full destruction of the wavelength,

2t = y/2

t = thickness of the coating material

y = wavelength in the coating material

But;

y = y_a/n; where y_a is wavelength in air

Substituting;

y = 529/1.2 = 440.83 nm

Then,

t = y/4 = 440.83.4 = 110.21 nm

Therefore, thickness of the coating material should be 110.21 nm.