Thin-film optics

[1] In order to exhibit thin-film optics, the thickness of the layers of material must be similar to the coherence length; for visible light it is most often observed between 200 and 1000 nm of thickness.

Layers at this scale can have remarkable reflective properties due to light wave interference and the difference in refractive index between the layers, the air, and the substrate.

This effect, known as thin-film interference, is observable in soap bubbles and oil slicks.

Examples include low emissivity panes of glass for houses and cars, anti-reflective coatings on glasses, reflective baffles on car headlights, and for high precision optical filters and mirrors.

[3] In buttercups, the flower's gloss is due to a thin-film, which enhances the flower's visibility to pollinating insects and aids in temperature regulation of the plant's reproductive organs.