The Surface of the Butterfly’s Wing

The striking metallic colours on the wings of some butterflies change depending on the angle from which they are viewed. The wing colour of one of the species is so pure and intense that it can be seen from 805 metres away. What makes the butterfly’s wing remarkable?

Consider the following:

Rows of tiny concave surfaces on the wings of a green swallowtail butterfly (Papilo blumel) reflect light in various. For example, the centre of concavity reflects yellow-green light, whilst the edges reflect blue light. Also, light at the centre of a concave surface is reflect directly, but light striking the sides first bounces through a surface of multiple layers, which amplifies and partially polarises, or rotates, the light waves. The final mix is called structural colour because of the complex way in which it is produced. It took ten years for researchers to produce a simplified replica of the butterfly’s wing surface. Such technology, they hope. will lead to bank notes and credit cards that are harder to forge and solar cells that more efficient at collecting energy from the sun. However, duplicating the surface of the butterfly’s wing is challenging. “Despite the detailed scientific understanding of optics,” writes professor Ullrich Steiner of Cambridge University’s Nanoscience Centre, “the astonishing varied colour patterns found in nature often surprises the optical effects than can be generated by the technological means”