Newton's soap bubbles reveal why thin films shimmer in color
The Colors of a Soap Film
A soap film thinner than a micrometer reflects light as a single cosine in wavenumber, so its color is simply white minus the cosine transform of the CIE color-matching functions evaluated at the optical path difference 2nd. The computed colors match the thickness table Newton compiled from watching bubbles under a glass cover. The model also explains the black spot where the two reflections cancel, and the purple bands that separate successive interference orders.
At d = 0 the cosine equals 1 at every wavelength, so the film reflects nothing: the two reflections cancel exactly.
- JKCalhoun
Loved the small book "Soap-Bubbles and the Forces Which Mould Them" [1], [2], [3] by C. V. Boys.
He talks about the colors of soap bubbles (among other things). After reading it I watched a large bubble-sheet exhibit at the Exploratorium in San Francisco with fascination—noting how the colors were different at the top of the film, (where it is thinner) compared with the lower part of the film (where it is thicker).
As the bubble begins to evaporate and get thinner, it eventually becomes colorless (black, I suppose) just before popping.
Aside from the section on color, the whole book is a beautiful example of reasoning, the scientific method, etc. (as though presented to Physics students—but it is nonetheless easy for the layman to follow along).
[1] https://archive.org/details/soapbubblestheir0000cvbo/
[2] https://archive.org/details/SoapBubbles-English-C.V.Boys/
- schobi
Invert the process - That would allow you to build a thickness gauge from just white light and 3 sensors. Or maybe add a few more (there are multislectral sensors from ams osram) for robustness.
Not sure why you would need that though..
Similar effect in devices to measure polarization of light. You introduce white light and crossed polarization filters. Depending on the amount of rotation similar colour patterns emerge. I haven't seen an automatic device yet, but manual evaluation of the colors
- grenoire
What a lovely gradient pattern.