In the figure below, light is incident perpendicularly on a thin layer of materi
ID: 1487309 • Letter: I
Question
In the figure below, 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 r3 (the light does not reflect inside material 2) and r4 (the light reflects twice inside material 2). The waves of r3 and r4 interfere, and here we consider the type of interference to be either maximum (max) or minimum (min). For this situation, n1 = 1.30, n2 = 1.57, n3 = 1.90, and L = 300 nm. Give the wavelength that is in the visible range. (State the visible wavelength when rays r3 and r4 undergo maximum constructive interference.)
Explanation / Answer
condition for constructive interference 2L = mn
thickness for which the constructive interference happens is given by = nn
= n2 (2L/m) = 2n2L / m
= 2 * 1.57 * 300 * 10-9 / 1
= 942 nm