I've observed that meta-lenses, which are constructed using nanostructures, exhibit different appearances at times.
Specifically, in Article 1, the meta-lens appears transparent as seen in the graphical abstract of Article All-Glass, Large Metalens at Visible Wavelength Using Deep-U...
Conversely, in Article 2, the meta-lens appears white, as depicted in the graphical abstract of Article All-Glass 100 mm Diameter Visible Metalens for Imaging the Cosmos
I've observed similar images in other studies as well, not just the examples mentioned above. I'm curious about the reasons behind this variability in appearance. Why do metalenses sometimes appear white instead of transparent?
Furthermore, I'm interested in whether there are any methods to make metalenses appear more like conventional lenses in their appearance.
Metalensler karmaşık renkler içerir. Bu renklerin birleşiminden beyaz renk oluşur. Örneğin cyan renginin beyaz rengi oluşturması için gerekli olan yardımcı renk ve magenta renginin beyaz rengi oluşturması için gerekli olan yardımcı renk farklıdır. Lensler ve metalenslerde bu renkleri doğadan alır.
Metalenses are made of transparent material just like any lens. What you see when you look at a lens is either a defocused version of what’s on the other side of the lens OR a distorted reflection of what is on the same side of the lens. All transparent materials have some reflection at each surface as described by the Fresnel coefficients. Layers of dielectric coating can reduce the reflection, but it is never zero. If the lens is uncoated (as metalenses often are) the reflection can be quite bright, particularly if you are at just the right angle to a light source. What you see depends on which is brighter: whats behind the lens or what’s in front. Often when making a photograph you shine bright lights on the subject.
Metalenses are also structured to work best at a particular wavelength of light. The effect of the metalens is determined by the size of the structures relative to the wavelength of light. If you make a metalens for IR, the size of the structures is wrong for visible light. In that case the overly large structures act more like scatterers and so the lens looks white.
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