The diagram below shows light incident perpendicularly on three thin layers of thickness L (the rays are shown inclined to the normal for clarity only). The indices of refraction of the thin layers and of the media above and below those layers are given. 1.6 1.4 1.8 1.4 1.6 1.4 1.8 1.8 1.6 (i) (ii) (iii) Consider only the light that emerges below the thin layers; light that has undergone no reflection at all, or two reflections, as indicated by the two transmitted rays in Figure (i). (a) For each case shown, what phase difference is introduced between the two transmitted light rays due only to reflection? (Do not consider the path difference.) (i) Phase difference = (ii) Phase difference (iii) Phase difference = (b) Consider situation (i) above with constructive interference for light transmitited through the thin layer. Determine an expression for & (the wavelength of light in vacuum) in terms of L (layer thickness), n (refractive index of the layer) and m (the order of interference).