57 through 68 Transmission through thin layers. In Fig. $35-43,$ light is incident perpendicularly on a thin layer of material 2 that lies between (thicker) materials 1 and $3 .$ (The rays are tilted only for clarity.) Part of the light ends up in material 3 as ray $r_{3}$ (the light does not reflect inside material 2 ) and $r_{4}$ (the light reflect insice inside material 2$)$ . The waves of $r_{3}$ and $r_{4}$ interfere, and here we consider the type of interference to be either maximum $($ max) or minimum (min). For this situation, each problem in Table $35-3$ refers to the indexes of refraction $n_{1}, n_{2},$ and $n_{3},$ the type of interference, the thin-layer thickness $L$ in nanometers, and the wavelength $\lambda$ in nanometers of the light as measured in air. Where $\lambda$ is missing, give the wavelength that is in the visible range. Where $L$ is missing, give the second least thickness or the third least thickness as indicated.