We know that thin-film interference creates colors by constructive and destructive interference of different wavelengths. One of the better images I refer to is this:
Though the example only traces one ray of light, a different ray striking at C can be seen to interfere with the first, so having just the original ray interfere with itself, completely neglecting the distance CD, is reasonable.
The path length through the medium results in different phase shifts for different wavelengths, ultimately resulting in different interference for different colors.
My question is, why don't we see this happen in thicker materials?
I have a guess:
For thicker materials, variation in surface perfection results in a wide range of light paths (a small change in
Aresults in large changes inB, which results in even larger changes inC), so everything averages out. This effect is strengthened by dispersion.If this is the case, are there examples of thick materials constructed with sufficient precision to show interference?
Best Answer
You don't see it happening with thicker films because the size of pupil of your eyes is finite (about 3mm) and as the layers become thick the distance between the 2 rays reaching your eyes increases so both of them cannot enter your pupil and there is no interfernce.