Based on the Bragg-Snell law, the photonic bandgap can be obtained and it seems to be similar to the reflected wavelength by thin-film interference. Can anyone elaborate what difference between them?
Dear Yuchen Zhu
You can see the following research:
1. https://natural.materials.drexel.edu/research-2/structural-color-and-polymer-thin-films/
2. http://www.iap.tuwien.ac.at/~gebeshuber/Gebeshuber_&_Lee_EoN_2015.pdf
3. https://www.tdx.cat/bitstream/handle/10803/671630/pfev1de1.pdf?sequence=1&isAllowed=y
Dear Saad,
Thanks for sharing these useful references and they are helpful to tell the difference between them. But what I am trying to figure out is how to determine where the iridescent colour comes from. Both thin-film interference and photonic crystal diffraction can yield the iridescent colour which is angle-dependent, and how do you distinguish them? I am looking forward to getting your response. @Saad Zahraw Sekhi
Dear Yuchen Zhu,
You are right that they look similar (thin-film interference is the result for 1D photonic crystal after all...)
I think that 2D and 3D photonic crystals introduce a type of angular dependance that is not seen with 1D; if you scan over a large range of angle of observation (for a fixed angle of incidence), you will probably see diffraction modes appearing (almost similar to different harmonics, on a wavelength scale). As well, there could be some back reflectance that would not be seen with 1D thin-film interference.
Photonic crystals should have less angular dependence than thin film interference. When you look at a Morpho butterfly wing you see only a clear blue color at all angles.
Dear Daniel and Nicholas,
Thanks for your elaborate answer and yes, it is true that thin-film interference is one of 1D photonic crystals. Here are attached figures to illustrate both of them (thin-film interference and 3D photonic crystal) are angle-dependent (colour shift as with varied angle) because the optical path difference created by them are subject to the angle of incident light. Let me take an example happening in our daily life, iridescent colour is observed when you cleaning your dishes because the oil film on the water surface. Opal demonstrates this colour as well because it is a well-organised periodic structure that diffracts lights. By virtue of our naked eye, how do we determine this iridescent colour is from thin-film interference or photonic crystals? Daniel Poitras
By the way, I feel the structure colour produced by a Morpho butterfly wing is due to the unique structure itself that shapes like a Christmas tree and every single beam of light hit on this structure does not alter the optical path difference. It means that blue colour is angle-independent in this butterfly wing. I can not say that is true but it is just hypothesis. Nicholas Edward Schlotter
I am grateful if you clear my doubt for these questions.
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