Question

A nonreflective coating (n = 1.35) covers the glass (n = 1.52) of a camera lens. Assuming that the coating prevents reflection of yellow-green light(wavelength in vacuum = 563 nm), determine the minimum nonzero thickness that the coating can have.

Answer 1

There is a phase change of (wavelength / 2) at both the front surface and the back surface of the coating ) and so the phase change can be ignored.

The path difference needed for the reflected rays to interfere destructively must be 1/2 a wavelength.

To get the 1/2 wavelength the thickness must be 1/4 of a wavelength AND the thickness can be less because the wavelength is shortened inside the coating because the waves slow down.

The result is that (wavelength / 2) =